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1.The notion of schema before Kant

Before considering in detail the reasons for why the notion of schema is problematic both in the work of Kant and also in more recent thinkers, an overview of the meanings in which this term was used before Kant has to be introduced.

The literature on the meanings of the notion of schema before Kant and their possible influences on him is very scarce. In the Historisches Wörterbuch der Philosophie a precise and detailed overview of the uses of the term is presented by Werner Steigmeier, although not aiming to stress the relations and influences between the authors, but rather to expose and list the variety of significances of the notion of schema throughout the history of philosophy. Although the overview provides a large contribution, it is not complete and important authors are omitted (for instance: Joachim Georg Darjes, Christian Thomasius, Johannes Nikolaus Tetens). Some relevant points are made by Thiel (2018), Psilojannopoulos (2013), Semplici (2011), who deal with Thomasius’ and Tetens’s conceptions of cognition and its relation to sensibility.

However, they do not investigate the relation of their doctrines with Kant’s schematism.

Given the absence of detailed researches on the notion of schema before Kant, I have decided to devote the first chapter to this task. More specifically, the chapter is divided into three sections, following the chronological order (ancient times, middle ages and modernity), in which ‘schema’ is found in philosophical literature. The variety of the connotations of this notion underlines that it does not possess a definite and specific meaning, although its use is relatively widespread and particularly in modern thinkers it is often referred to as addressing a mediating function between the activity of the understanding and the passivity of sensibility. I have devoted more attention to presenting the uses of the term ‘schema’ in Darjes, Thomasius and Tetens because of their influence on Kant with regard to various philosophical questions - although it is difficult (if not impossible) to prove that they specifically influenced his account of schematism -.

The concept of a schema has a long and complex history. It is a philosophical concept whose meaning has been shaped by its history; we would do well in making ourselves acquainted with that history in order to prepare ourselves for the discussion.←23 | 24→

1.1 Ancient times

In ancient times, ‘schema’⁴ possessed the meanings of form, appearance, shape and it was used in philosophical literature with different connotations: rhetorical (Plato, Aristotle), moral (Plato), geometrical (Plato), logical (Aristotle), ontological (Leucippus, Democritus, Theophrastus, Aristotle), epistemological (Proclus), and physical (Philo of Alexandria). In the 5th century BC we find the first uses of the term in Leucippus and Democritus with an ontological connotation: it indicates the atom’s form and surface (Aristotle, De Democrito Frg, 208; Rose=Vs 68, A37), which are features of the atoms that are held together with movement, position in space and time and colour, whose possibility of variety has no limitations (Aristotle, De gen. et corr. I, 1, 315 b6; Rose=VS 67, A9). In a different, namely rhetorical sense, Plato refers to ‘schemata’ as figures of speech:

“[…] for not by art or knowledge about Homer do you say what you say, but by divine inspiration and by possession; just as the Corybantian revelers too have a quick perception of that strain only which is appropriated to the God by whom they are possessed, and have plenty of dances (σχηµάτων) and words for that, but take no heed of any other.” (Plato, Ion. 536 c, transl. W.R.M. Lamb.)⁵

In the above-mentioned passage, Socrates uses a metaphor to describe Ion’s competence concerning Homer’s poetry: just like the Corybantic revelers possessed by the gods are able to improvise dances⁶ and poetical forms (σχηµάτων), so Ion is possessed by Homer’s verses. Therefore, schema means artistic composition of words, poetical structures.

But Plato uses the term also with a different meaning, dealing with behaviour and action. In Epinomis, the dialogue dedicated to the various kinds of knowledge and to the nature of virtue, he writes:

“For these things (desire of knowledge and virtue) are not easily engendered, but when once they are begotten, and receive due nourishment and education, they will be able to restrain the greater number of men, even the worse among us, in the most correct way by our every thought, every action, and every word about the gods, in due manner and due season, as regards both sacrifices and purifications in matters concerning gods ←24 | 25→and men alike, so that we are contriving no life of pretence (σχήµασι), [989d] but truly honouring virtue, which indeed is the most important of all business for the whole state.” (Plato, Epin.989 c.-d, transl. W.R.M. Lamb.)⁷

Here the first rhetorical use of the notion turns into a moral one, indicating external features and misleading behaviours, in opposition to honesty⁸. This reference to ‘schema’ as a feature which might not mirror the truth but, instead, falsity and appearance of things, is found also in other lines of Plato’s works (Plato, Resp. 365 d; Resp, 529 d.) with a more philosophical connotation. Moreover, in Timeo the term ‘schema’ is used to point to the geometrical figure (Plato, Tim, 53 b). In this sense, the notion is found also in some passages of Aristotle (Aristotle, De ani II. 3, 414, b 20–32).

Aristotle’s primary uses of the term are either in metaphysics (Rohr 2017, pp. 7–17), namely for clarifying his notion of form - morphē, eidos - (Aristotle, Phys VII, 3, 246 A I; De part. anim. I. I. 640, b 33.), or within his logic, in order to address the syllogism’s figures: “[…] all the syllogisms are imperfect, and are completed by means of the figures (σχημάτων) mentioned.” (Arist. Apr, I, 19, transl. J.Jenkinson)⁹

This passage is only one example of many in the Prior Analytics, in which the term ‘schema’ is found. In this work, Aristotle focuses on his theory of the syllogism, whose propositions (premises and conclusion) consist of a major, a minor and a middle term, which joins these premises and whose position determines the schema, namely “figure” of the whole syllogism. Interestingly enough, this Aristotelian use of the noun ‘schema’ as a middle logical term was used not only during the Middle Ages, but also in modern logic¹⁰.←25 | 26→

Theophrastus gives Aristotle’s view a more scientific rather than metaphysical bent. In his work on sensibility (On Sense Perception - Περὶ αἰσθήσεων -) he compares Democritus and Plato’s theories. He states that while both Plato and Democritus separate sensibility and understanding, Democritus does not ascribe an objective status to perception, since it merely depends on the subject’s sensible modifications. In contrast, objectivity is provided by a principle (archē), which consists in indivisible elements that cannot be grasped through the senses, namely the atoms, which are objects of the understanding and have quantitative and measurable features such as their size, dimension and shape or ‘schema’ (Thphr. Sens. 65–66).21

Later on, Philo of Alexandria uses the notion to describe the physical external shape of things (Philo. Alex, De op. m. § 120), while Proclus attributes to ‘schema’ a new original, epistemological sense, which is close to that of Kant: it does not refer to external features of things or linguistic or logical structures, but rather to representations, which mediate between things and concepts, sensibility and intellectual activity (Proclus, In Euc., 51, 21, 94, 25). There is no evidence to support a direct, historical lineage to Kant, although the similarity of the two perspectives is impressive.

1.2 Middle Ages

According to several studies¹¹ during early medieval times, the Greek term ‘schema’ was translated by logicians into the Latin noun figura which derives from the verb fingĕre (modelling, shaping, giving form) and came to be used to talk about symbols, allegories, rhetorical figures¹² and qualities as well as to indicate the visible appearance of a person or the visible and tangible form of anything. But it was in its logical use, which refers to the Aristotelian ‘syllogistic figures’, that the noun became widespread in the philosophical works of these times. In Aristotle’s Lyceum, ‘schema’ was used to talk about the syllogistic figures. The oldest translation of the Greek ‘schema’ into the Latin ‘figura’ can be found in a passage from Cicero’s Brutus:

“The Greeks themselves acknowledge that the chief beauty of composition results from the frequent use of those mutated forms of expression which they call tropes, and of those ←26 | 27→various attitudes of language and sentiment which they call schemata [figures].”(Brut., 69, transl. E. Jones)¹³

Another example of the synonymy and interchangeability of ‘schema’ and ‘figura’ is found in Augustin’s allusion to modes of speech, in his explanation of the term ‘enigma’:

“Chapter 9. - Of the Term Enigma, And of Tropical Modes of Speech. 15. What has been said relates to the words of the apostle, that we see now through a glass; but whereas he has added, in an enigma, the meaning of this addition is unknown to any who are unacquainted with the books that contain the doctrine of those modes of speech, which the Greeks call Tropes, which Greek word we also use in Latin. For as we more commonly speak of schemata than of figures, so we more commonly speak of tropes than of modes.”(De trinitate, XV, IX.15, transl. A. W. Haddan)¹⁴

However, there are some controversies on the translation of the term ‘schema’ into ‘figure’ or ‘form’: the first being the Aristotelian figure of the syllogism, whilst the second concerns the logical form.

For example, taking Boethius (475/477 – 524/526), who translates Aristotle’s Prior Analytics as well as the Topics: he develops in his main works, namely De syllogismo categorico, Introductio ad syllogismos categoricos, De hypotheticis syllogismis (Boethius 1882–1891) a theory on the hypothetical syllogism and modifies the figures (schemata) of syllogism by changing the translation of the copula used by Aristotle (Boethius uses the verb: “to be”, instead of the more literal “to belong”).←27 | 28→

This concept of schema as figura syllogismi is present also in the Dialectica (Abelard 1970) written by Peter Abelard which is completely based on Boethius’ theory of logic except for the introduction of an innovative method in reducing the four standard figures (called ‘schemata’), to the first one. Moreover, in a work wrongly attributed to Thomas Aquinas, the term ‘figura’ indicates the middle term which determines the structure of the judgement¹⁵.

Later on, William of Ockham and John Buridan also used the noun ‘schema’ to indicate the figure of the syllogism. More specifically, the former, in his Summa logicae (Ockham 1974) proposes to substitute Aristotle’s method to prove syllogisms’ figures (ekthesis) through the use of a particular syllogism (called expository), in which the middle term (which determines the form or schema of the syllogism) is the subject of both premises. While the latter develops in his Summulae de Dialectica (Buridan 1487) and in Consequentiae (Buridan 1493) a theory of syllogism, considered as a kind of formal consequence, distinguished in figures (or ‘schemata’), the conclusion of which might be direct or indirect (i.e. the minor term is predicated of the major).

This logical connotation of the noun endures in the Modern Ages also. However, it comes to possess also a new, epistemological sense, which later on develops and flourishes especially in the works of Kant.

1.3 Modern Ages

Differing from the Middle Ages, the notion of schema in the Modern Ages returns to hold a variety of non-logical connotations: figurative (Wolff), rhetorical (Sturmius, Diderot, D’Alembert), biological (Ploucquet), physical (Bacon) and epistemic (Thomasius, Darjes, Tetens).

References to the use of the term are present in Rudolph Goclenius’s work (1547–1628) who relates it to ‘figure’ in two senses: first, in a geometrical sense and secondly, in a rhetorical one, which finds support in the work of Ioannes Sturmius (1507–1589), who defines ‘schema’ as argument, structure of discourse: “[…] schemata are arguments directed to prove and amplify, as similarities and examples.” (Goclenius 1613, p. 579, transl. L.S.)¹⁶←28 | 29→

A more philosophical connotation is attributed to the term by Francis Bacon, who uses the notions ‘schematismus’ and ‘meta-schematismus’ (Bacon 1620, I, pp. 45–5) to indicate the structure of matter and its changes:

“The human understanding is carried away to abstraction by its own nature, and pretends that things which are in flux are unchanging. But it is better to dissect nature than to abstract; as the school of Democritus did, which penetrated more deeply into nature than the others. We should study matter, and its structure (schematismus), and structural change (meta-schematismus)” (Bacon 1620, I, p. 51, transl. M. Silverthorne)¹⁷

In contrast with metaphysics, which looks for forms and essences beyond experience, he aims at elaborating a new method in philosophy, intended as an actual science, which works through the help of observations and experiments and aims to discover objective properties of nature. This last one is seen in its material process of formation (natura naturans), which has to be distinguished from all those characteristics (idola) added by the activity of understanding and fantasy, which have the tendency to go beyond experience, thus generating illusions and mistakes.

Christian Thomasius provides another - and highly interesting for our purposes - epistemic use of the noun ‘schema’. According to him, cognition begins with the influence of the objects on our senses, which leads to the constitution of schemata, regarded as a kind of Cartesian material ideas as the basis of cognition:

“Thinking is an act of the mind, in which man - or the mind in the brain – through schemata impressed in the brain by the movement of external bodies via the sensible organs, affirms, negates or asks for something, through discourse and constant words of orations.” (Thomasius 1688, pp. 83–84, transl. L.S.)¹⁸

This process through which ideas are constituted is not only passive, but also active, as can be seen from what Thomasius attributes to the faculty of understanding:

“[…] but we must not forget also their Entium rationis, that have the only and unique essence within human understanding. These are nothing more than the expressed schemata or ideas of actual things and their unification or separation, which are realised through the understanding. When the understanding joins together the same ideas and ←29 | 30→separates the different ones and gives a place to each one, this is called ens logicum or metaphysicum.” (Thomasius 1691, pp. 131–132, transl. L.S.)¹⁹

Since no schema is possible without the activity of the understanding, material ideas can be described as the first elements implied in the process of cognition, constituted both by passivity (the matter provided by the external world) as well as activity (the unification and diversification of the understanding):

“§ 13. Because the truth is nothing more than a coincidence of the human mind and the nature of things outside those thoughts. § 14. Here you have not to ask whether the mind must or must not correspond to things […] § 15. For the things are such that they can be understood by humankind and the mind is made in a way that it can grasp the external things. § 16. The external things cause impressions on human understanding. This, then, considers these touches, separates them and puts them together.” (Thomasius 1691, pp. 139–140, transl. L.S.)²⁰

This theory shares similarities with Kant’s (as well as the Lockean²¹) perspective: firstly, all assert that the process of cognition begins from the senses; ←30 | 31→secondly, they underline the necessity of both passive and active faculties; thirdly, they describe the activity of understanding in terms of unification and separation and finally, they define the role of the schemata as functions in the middle between passivity and activity. As Psilojannopoulos (2013) states²², these theoretical similarities with the doctrine of Kant are also reflected in terminological ones, thus providing circumstantial evidence to the claim that Kant knew Thomasius’ Einleitung zu der Vernunftlehre²³.←31 | 32→

Later on, the term can be found in the works of Christian Wolff, who uses it not in an epistemic, but rather in the more common figurative sense, namely as a framework to represent a relation. More specifically, he refers to relations among relatives through a “schema of parenthood” - “schema cognationis”- (Wolff 1747, pp. 416–17).

In contrast to Wolff, his disciple Joachim Georg Darjes²⁴ uses the noun with a meaning connected to material ideas. Like Thomasius, he explains the process of cognition, stressing that the spontaneous being (the soul) is affected by external things, which leave material ideas in the brain. To have ideas, a medium between the soul and the external substances must be presupposed, that is the schema (Tonelli 1994): “[…] this schema of perceptions, mentioned above, is the only link of passive and active entities.” (Darjes 1743, par. 326, transl. L.S.)²⁵

The soul, which is a simple and purely active essence, is affected by the senses thereby producing perceptions materialiter spectatae (Darjes 1743, par. 124) but for cognition to arise, these perceptions need to be moulded by schemata, which are mediating functions between the active soul and the passive sensibility. Then, through a process of confrontation and abstraction, general concepts can be produced by the soul’s operation. Cognition, therefore, begins with the senses, with the experience of single objects and then develops through processes of abstraction led by the understanding’s activity through attention and reflection (Psilojannopoulos 2013, pp. 252–253; Lorini 2011, p. 282). In this interpretation of the concept of schema as a medium between the receptivity of the senses and the activity of the understanding, we can see Darjes anticipating an important aspect of Kant’s account. More specifically, Darjes describes here what Kant discusses when he considers concrete, empirical examples of schematising concepts.

Besides this epistemic connotation, the use of ‘schema’ in the philosophical literature of the modern age is still linked to the arts of rhetoric and speech, as it is stated in the Encyclopedie, where ‘schemata’ are seen as instruments of the mnemotechnique, methods used to increase the capacities of memory.

“[…] because for sure our imagination is of great help to our memory, it is not possible to reject the method of schematisms, given that images have nothing extravagant or puerile about them and that they are not applied to things which are not amenable to them.” (Diderot & d’Alembert 1751–1780, transl. L.S.)²⁶←32 | 33→

Differently, namely in reference to biology and physiology, ‘schema’ is used by Ploucquet to indicate the body’s organisation, thus underling once again the function of schemata as a medium between activity and passivity: a body is a material entity provided with an activity giving it organisation: “[…] experience teaches and [the faculty of] reason deduces that bodies are organised in themselves and have a natural capacity to modify themselves in others schemata.” (Ploucquet 1764, par. 399, cap. XVI, transl. L.S.)²⁷

But aside from these rhetorical and biological connotations, the term is used again epistemologically by Johann Nicolas Tetens. In his Philosophische Versuche²⁸, a work which was open on Kant’s desk when he was writing the Critique (as Johann Georg Hamann²⁹ states in a letter to Johann Gottfried Herder on 12th May 1779). Tetens, often called the “German Locke”³⁰, deals among other things with the relation between the soul and the body and the sources and development of human cognition. He follows Darjes’ terminology of a ‘schema perceptionis’³¹, but regards it as a physical centre of unification of all the data of ←33 | 34→experience, referred to as “material ideas”: “[…] with each manifestation of the soul a certain inner part of our body acts; we can call this part the brain, sensorium commune, the organ of the soul, schema perceptionis or what else.” (Tetens 1777, II 158, transl. L.S.)³²

Schemata are regarded as synonyms for sensorium commune or “organ of the soul”, expressions possibly influenced by Charles Bonnet (quoted several times by Tetens) and meant to identify the part of the brain in which ideas are traced and combined. In his L’Essay de Psychologie (1755), Bonnet describes the natural production of ideas from infancy and states: “ideas are nothing but natural signs, and these signs are images traced by objects on the brain.” (Bonnet 1755, VII, p. 13, transl. L.S.)³³ Ideas are sensible traces of the objects and it is only through the use of language that abstract thought and universalisation are possible. In this view, the soul can be compared to a musician that plays on the brain (siege de l’ame) but lies in itself beyond any empirical evidence:

“[…] the seat of the soul is a little machine, prodigiously composed and very simple in its composition. […] It is possible to represent this admirable instrument of the operations of our soul with the image of a harpsichord, an organ, a clock or that of another, more composed machine. […] the soul is the musician, which performs on this machine different tunes or judges those that are played and that he repeats.” (Bonnet 1755, Ch IV,9, transl. L.S.)³⁴

However, in order to better understand Tetens’s conception of schemata, whose importance for our purposes lies on his influence on Kant, a deeper inquiry of his doctrine of cognition is needed.

1.3.1 Tetens’s conception of schema

In order to clarify the meaning of the notion of schema in Tetens’s Philosophische Versuche, it is important to focus on his account of the cognitive process.←34 | 35→

In my analysis I will concentrate on three main aspects of his viewpoint: 1) the distinctions among three main faculties; 2) the activity and passivity as characteristics of the cognitive process; 3) the dualism between body and soul, which is expressed by two main claims, namely that there is a correlation between psychological and physical changes and that the soul has an independent and own activity.

Tetens underlines in the opening of the first Essay the distinctions of the three main faculties: “The soul feels, has representations of things, properties and relations and thinks.” (Tetens 1777, I, 1, transl. L.S.)³⁵

These faculties are: Gefühl (the faculty of feeling), Vorstellungskraft (the faculty of representation) and Denkkraft (the faculty of thinking). Feeling is something hard to grasp in itself. It is a complex manifestation of the activity of the soul, which cannot be explained fully: “Then, what is to perceive or to feel? Here I have to confess my inability to explain it. It is a simple manifestation of the soul, which I am not able to divide into more subtle manifestations.” (Tetens 1777, I 170, transl. L.S.)³⁶ Since it is impossible to provide a direct and conclusive characterisation of feeling, Tetens proposes to clarify the characteristics of this basic faculty through an analysis of its objects: impressions, that are, first of all, actual modifications of the subject. We can feel only something that is present and characterised by intensity, duration and extension. Therefore, he agrees, although only partially, with the traditional view of sensibility as a passive faculty:

“What is immediately felt is always, where this modification of the soul could allow itself to be observed, something passive […]. It is never the activity in itself, never the effort itself that we immediately feel; it is a durable consequence of something that is not produced from our spontaneous strength [capacity], but that has been already be produced when it is the object of a feeling; […]” (Tetens 1777, I, pp. 173–174, transl. L.S.)³⁷

This capacity of being affected does not consist only in a mere passivity, but it is at the same time, a kind of activity similar to a reaction. As the body reacts ←35 | 36→to external stimuli, so does the soul as it receives impressions. Each impression modifies the soul, thus leaving a sort of trace, a representation, regarded as a sensible sign of the impressions of the objects affecting our senses:

“[…] these are representations of other objects; modifications, which represent something else and, when they are present, they allow us to see and know not only themselves but also their objects.” (Tetens 1777, I, p. 15, transl. L.S.)³⁸

Since representations are based on impressions, the representational theory of Tetens does not part from the traditional, associative empiricism. However, the associative view of mental activity is only the starting point of his research. Primary sensations represent the objects in the way in which they are perceived (facultas percipiendi). Yet, the soul can exercise an activity through these first representations, since it can reproduce (fantasia) and combine them in new ways (facultas inventiva). Moreover, imagination owns a particular productive power: while its reproductive side can only call upon past impressions; its productive one can provide data of experience with a new order. It acts on impressions comparing them to each other and analysing, breaking down each one into its elements in order to produce simpler representations, which are not evident at first sight of the complex given perceptions. In this process, past representations (phantasmata) can be recalled but they are not sufficient to determine objects of thought (ideas), regarded as unities related to each other through thinking and reasoning. However, the representations provided by imagination are in themselves only a sort of matter provided by sensations and they still lack form:

“Representations turn into ideas and thoughts, but considered in themselves, they are not. The image of the moon is only the material for the idea of the moon; it still lacks form: the idea contains, beyond the representation, a consciousness, perception and distinction and presupposes comparisons and judgements, when regarded as an idea of a certain object.” (Tetens 1777, I, p. 26, transl. L.S.)³⁹

This leads us to the second main aspect of his account: a superior faculty, the understanding, is needed to unite the representations as a whole, providing them with an intelligible and objective character.←36 | 37→

The faculty of imagination, according to Tetens, places itself between sensibility and understanding, between passivity and activity, therefore sharing similarities with the view of Kant. However, their accounts are not fully identical because Kant asserts that the productive imagination is a synthetic a priori function. As de Vleeschauwer underlines: “[…] the reproductive function is […] examined in its constitution and psychological activity and it is distinct from the way in which Kant dealt with it, mostly for the absence of the reference to a synthetic capacity.” (de Vleeschauwer 1934–1937, II, p. 97, transl. L.S.)⁴⁰

Moreover, through his doctrine of the constitution of knowledge, Tetens opposes empiricism, relying on non-sensory functions (understanding, the soul, and apperception) as necessary conditions for developing an objective knowledge and unifying ideas: sensible data provided by experience need a common referent, an understanding, in order to be united and compared. Since this obscure unity is not in itself an impression, but a core unity to which all the impressions are referred, it has to be thought of as something immaterial, which holds an obscure feeling of awareness of its permanence, of its identity:

“[…] the idea or representation of my ´I` is not a collection of individual representations that our imagination might have turned into a whole just like it unifies the individual representations of soldiers into a representation of one regiment. That unification lies in the impression itself, in nature, and not in a combination that makes itself. For this reason a representation of ne subject with different features arises, that is, a representation that immediately arises from the impression, must be thought in this way and turned into an idea such that the common human understanding actually does from it in this way.” (Tetens 1777, pp. 394–5, transl. Watkins 2009, pp. 370–1)⁴¹

Through his doctrine of the ‘I’, Tetens distances himself from empiricism. As Thiel declares, three notions of the self can be distinguished in Tetens’s account. Firstly, the empirical, psychological self of the inner sense; secondly, the metaphysical ←37 | 38→self, as an immaterial entity that intends to collect all powers and operations of the human being; finally, the unitary self as a condition of the mental activity. In this third connotation the ‘I’ is regarded as a non-empirical function, as a necessary condition to develop an objective knowledge and unify ideas. Since each experience is related to this obscure but always present unity, Tetens rejected the Humean doctrine of the ‘I’ as a stream of sensations. The ‘I’ cannot be considered as a mere sum of representations, because the condition required to have them lies exactly in their reference to a common unity distinguished from them:

“[…] in order to have representations of external objects, an activity of judging or forming propositions is required, and that in order to be able to do the latter, an activity of distinguishing between the external thing, the representation, and one’s own self is required. […] it is the notion of something that we have to think in order to be able to explain representations of external objects. Without such a notion of the self, as distinct from the representations of other things, the possibility of forming propositions about the existence of external things could not even be entertained. This notion is a requirement of thought.” (Thiel 2018, pp. 70–71)

Tetens connects his epistemological dualism with a traditional Cartesian, ontological dualism. In his view, human nature consists of both a material and an immaterial aspect which form a union or interact with one another: “[…] in the human essence, beyond the bodily organ, a simple, non-corporeal essence, an actual, substantial unity can be found, which is properly the thing that perceives, thinks and wants.” (Tetens 1777, II, p. 210 transl. L.S.)⁴²

More specifically, he explains this dualistic interactionism by means of two basic propositions:

“[…] with each manifestation of the soul a certain inner part of our body acts; we can call this part the brain, sensorium commune, the organ of the soul, schema perceptionis or what else. The other basic truth is: there is beyond our bodily organs of the soul an essence, that acts in conjunction with each thing, but that is in itself an autonomous, permanent substance, that we call soul in a psychological meaning or our ‘I’.” (Tetens 1777, II p. 158, transl. L.S.)⁴³←38 | 39→

While each mental process is causally connected to a bodily process (as the first proposition states), the unity of representations also requires the action of an immaterial self or ‘I’ (as per the second proposition)⁴⁴. That is not a claim provided with necessity, but a reasonable hypothesis that cannot be falsified or demonstrated through observation. Tetens describes the first sentence as clearly empirical and claims that the second one requires “more reasoning”- “mehr Raisonnement” (Tetens 1777, II, p. 158, transl. L.S.) for becoming certain but emphasises at the same time that both propositions use concepts derived from sensation (ibid.) The evidence for the first sentence is, according to Tetens, clear and almost unnecessary to state: “Physiology and psychology have collected so many facts, which provide evidence of the modifications of the brain in contemporaneity with all modifications of the soul, that this proof can be considered without any doubt.” (Tetens 1777, II, pp. 159, transl. L.S.)⁴⁵

Against this background Tetens regards the schema perceptionis not only as something that mediates between sensibility and understanding, but also as the physical centre of unification of all the data of experience. Unfortunately, observation cannot inquire fully and completely the nature of these ideas. It is only possible to affirm that experience teaches that our organs are constituted by nerves, in which it is probable (but not observable), that a fluid matter or vital spirits flow. In his view, this process provides the physiological correlate or basis for ideas, which are therefore called “material ideas” - “materielle Ideen” - (Tetens 1777, I, p. vii, transl. L.S.). The existence of such ideas is postulated as reasonable hypothesis. What is important, however, is that material ideas, just like representations as they are observed through inner sense, need to be unified. That is precisely what the sensorium commune or the schema perceptionis does. The interpretation of schema as mediating function linking passivity and activity, senses and cognition opens out one path towards Kant’s epistemic use of the notion. But Tetens was not the author of this notion of schema: Darjes, as it has already been stressed, uses this noun in an epistemic sense also. Bonnet although he himself does not use the word ‘schema’, plays a relevant role as well in the ←39 | 40→development of the research on a middle function between understanding and sensibility and an equivalent or at least concept similar to ‘schema’ can be found in his work, namely sensorium commune.

1.4 Conclusion

What are the main results of this historical survey? Firstly, the analysis of uses of the notion of schema in the philosophical literature before Kant shows how it does not possess a unique meaning but is employed in different, albeit related, ways. Secondly, although this notion has manifold connotations (shape, figure, example, form) and applications (logical, rhetorical, ontological, biological), it can be generally regarded as a function of mediation and order. Thirdly, what is remarkable is that the expression ‘schema’ and its cognates in other languages is often part of more complex, linguistic constructions (such as schema perceptionis) or it is used more as a way to define terms rather than something that requires explicit definition itself. It is regarded as a synonym for a figure of speech, “life of pretence”, arguments, or it is used to describe the process of the constitution of ideas and then referred to as schema perceptionis (i.e. in reference to perceptions, and not as an autonomous term). ‘Schema’ is not treated as a separate topic of its own, but rather it is used in the definition and explanations of other concepts and ideas. This lack of interest in defining the notion has probably led to the multiplicity of its meanings in different contexts. As we will see in the subsequent chapters there are similarities between Kant’s conception and certain aspects of the views of predecessors such as Thomasius, Darjes and Tetens⁴⁶.

Kant might be accused of having disregarded the accounts of his predecessors concerning the notion of schemata. In the Critique of Pure Reason he makes several references to Plato, Aristotle, Bacon and Tetens, but none of these are devoted to the topic of schemata. However, Kant will build a doctrine of schemata whose meaning finds, in the Critique of Pure Reason, its greater epistemic and philosophical expression and complexity. It can be used as a main element for explaining the possibility of objective knowledge and the relation between sensibility and understanding. I shall show that Kant has the merit to have provided schemata with a definition (or definitions) and a precise role in his thought.←40 | 41→

4 From skhein, aorist of ekhō (whose general meanings are: to have, to hold, to keep).

5 “[…] οὐ γὰρ τέχνῃ οὐδ’ ἐπιστήµῃ περὶ Ὁµήρου λέγεις ἃ λέγεις, ἀλλὰ θείᾳ µοίρᾳ καὶ κατοκωχῇ, ὥσπερ οἱ κορυβαντιῶντες ἐκείνου µόνου αἰσθάνονται τοῦ µέλους ὀξέως ὃ ἂν ᾖ τοῦ θεοῦ ἐξ ὅτου ἂν κατέχωνται, καὶ εἰς ἐκεῖνο τὸ µέλος καὶ σχηµάτων καὶ ῥηµάτων εὐποροῦσι, τῶν δὲ ἄλλων οὐ φροντιζουσιν.”

6 Catoni (Catoni 2013), focuses on the meaning of ‘schema’ in relation to the ancient view of arts and dances as processes of sensibilisation of what belongs not to sensibility.

7 “[…] ταῦτα γὰρ οὔτε ῥᾴδια φύεσθαι, γµενάότε, καὶ τροφῆς καὶ παιδείας τυχόντα ἧς δεῖ, τοὺς πλείστους αὐτῶνκαὶ χείρους κατέχειν ὀρθότατα δύναιτ’ ἂν τῷ φρονεῖν καὶ πράττειν καὶ λέγειν περὶ θεοὺς ἕκαστα ὡς δεῖ τε καὶ ὅτε δεῖ,περὶθυσίας τε καὶ καθαρµοὺς τῶν περὶ θεούς τε καὶ ἀνθρώπους, οὐ σχήµασι τεχνάζοντας, ἀλλὰ ἀληθείᾳ τιµῶντας (d.) ἀρετήν, ὃ δὴ καὶ µέγιστόν ἐστι συµπάντων πάσῃ τῇ πόλει.”

8 However, since this dialogue was not written by Plato, the rhetorical use of the term has to be considered as a more central Platonic one.

9 “[…] δῆλον δὲ καὶ ὅτι πάντες ἀτελεῖς οἱ συλλογισμοί, καὶ ὅτι τελειοῦνται διὰ τῶν προειρημένων σχημάτων.”

10 Russell uses it to indicate propositional functions: “A propositional function […] may be taken to be a mere schema, a mere shell, an empty receptacle for meaning, not something already significant” (Russell 1919, p. 157) and later Tarski refers to syntactic schemata in his paper on truth definition (Tarski 1983, p. 157; p. 160; p. 172).

11 Van Deusen 2011, p. 189; http://www.etymonline.com/word/figure.

12 “Ornari orationem Graeci putant, si verborum immutationibus utantur, quos appellant τρπους, et sententiarum orationisque formis, quae vocant σχήματα”.

13 Another expression related to ‘schema’ and ‘figura’ is ‘species intelligibilis’, that is the first Latin translation (made by Cicero) of the Platonic ‘idea’. This notion is related to ‘schema’, insofar as it was used to address a mediating function of cognition by Thomas Aquinas: “on the one hand, it is a reality in itself, which is particular and individual, while on the other hand, it is a similitude, which is universal. Therefore, Thomas claims, the species as individual entity is capable of providing universal knowledge: it is singular and accidental in itself, but it also enables the human intellect to attain knowledge of universal essences.” (Spruit 1994, p. 169)

14 “9. - 15. Haec dicta sunt propter quod ait Apostolus, nunc per speculum nos videre. Quia vero addidit, in aenigmate; multis hoc incognitum est qui eas litteras nesciunt, in quibus est doctrina quaedam de locutionum modis, quos Graeci ‘tropos’ vocant, eoque graeco vocabulo etiam nos utimur pro latino. Sicut enim ‘schemata’ usitatius dicimus quam ‘figuras’, ita usitatius dicimus ‘tropos’ quam ‘modos’. Singulorum autem modorum sive troporum nomina, ut singula singulis referantur, difficillimum est et insolentissimum latine enuntiare.”

15 “Figura enim est dispositio medii secundum subjectionem et praedicationem, quae scilicet dispositio tripliciter variatur.” (Anonymous 1864)

16 “Schemata argumentosa, directa ad probandu et amplificandu, ut sunt similitude et exemplu.”

17 “Intellectus humanus fertur ad abstracta propter naturam propriam; atque ea, quae fluxa sunt, fingit esse constantia. Melius autem est naturam secare, quan abstrahere, id quod Democriti schola fecit, quae magis penetravit in naturam, quan reliquae. Materia potius considerare debet, et eius Schematismi, et Metaschematismi.”

18 “Cogitatio est actus mentis, quo homo vel mens in cerebro de schematibus a motu corporum externorum per organa sensuum cerebro impressis aliquid per modum discursus et orationis verbis constantis vel affirmat vel negat vel querit.”

19 “[…] aber wir müssen auch derer Entium rationis nicht vergessen, die in des Menschen Verstand einzig und alleine ihr Wesen haben. Diese sind nichts anderes als die eingedruckten schemata oder Idee von denen wircklichen Dingen und derer Zusammensetzung oder Absonderung die vermittelst des Verstandes geschehen. Wenn der Verstand die gleichen ideas zusammen fügt und die ungleichen voneinander sondert und ein jedes gleichsam an seinen gehörigen Ort bringet so nennt man es Ens rationis Logicum vel Metaphysicum.”

20 “§ 13. Denn die Wahrheit ist nichts anders als eine Übereinstimmung der menschlichen Gedanken und die Beschaffenheit der Dinge außer denen Gedanken. § 14. Hier musst du aber nicht fragen ob der Verstand mit den Dingen oder die Dinge mit dem Verstande überein kommen müssen […]. § 15. Denn die Dinge sind so beschaffen, daß sie von dem Menschen begriffen werden können und der Verstand ist so beschaffen daß er die äußerlichen Dinge begreifen kann. § 16. Die äußerlichen Dinge rühren die Empfindlichkeit des menschlichen Verstandes. Dieser aber betrachtet diese Berührungen theilet sie ab und setzt sie zusammen.”

21 As Locke famously states in his An Essay Concerning Human Understanding: “All ideas come from sensation or reflection. Let us then suppose the mind to be, as we say, white paper, void of all characters, without any ideas: — How comes it to be furnished? Whence comes it by that vast store which the busy and boundless fancy of man has painted on it with an almost endless variety? Whence has it all the materials of reason and knowledge? To this I answer, in one word, from EXPERIENCE. In that all our knowledge is founded; and from that it ultimately derives itself. Our observation employed either, about external sensible objects, or about the internal operations of our minds perceived and reflected on by ourselves, is that which supplies our understandings with all the materials of thinking. These two are the fountains of knowledge, from whence all the ideas we have, or can naturally have, do spring.” (Locke 1690, Book 2, Ch. 1, Par. 4). However, as Psilojannopoulos (Psilojannopoulos 2013, p. 40) stresses, it was Thomas Aquinas, rather than Locke, who influenced Thomasius through his claim that nothing comes in cognition that was not before in the senses: “Nihil est in intellectu, quod non prius fuerit in sensu.” (Aquinas 1258, Art. II, 3).

22 Possibly, Kant was influenced by Thomasius. Thus, Psilojannopoulos underlines the linguistic similarities of the following passages: “§ 13. Denn die Wahrheit ist nichts anders als eine Übereinstimmung der menschlichen Gedancken / und die Beschaffenheit der Dinge außer denen Gedancken. § 14. Hier musst du aber nicht fragen / ob der Verstand mit den Dingen / oder die Dinge mit dem Verstande überein kommen musten / sondern diese harmonie ist so beschaffen / daß keines des andern sonderliche Richtschnur ist / sondern die harmonie von beyden zugleich präsupponiert wird / außer daß die äußerlichen Dinge gleichsam den Anfang zu derselben machen. § 15. Denn die Dinge sind so beschaffen / daß sie von dem Menschen begriffen werden können / und der Verstand ist so beschaffen / daß er die eu- serlichen Dinge begreifen kann § 16. Die äußerlichen Dinge rühren die Empfindlichkeit des menschlichen Verstandes. Dieser aber betrachtet diese Berührungen / theilet sie ab / und setzt sie zusammen / sondert sie voneinander und hält sie gegeneinander.” (Thomasius 1691, pp. 139–140) Psilojannopoulos connects these passages to the famous Kantian lines: “Dass alle unsere Erkenntnis mit der Erfahrung anfange, daran ist gar kein Zweifel; denn wodurch sollte das Erkenntnisvermögen sonst zur Ausübung erweckt werden, geschähe es nicht durch Gegenstände, die unsere Sinne rühren und teils von selbst Vorstellungen bewirken, teils unsere Verstandestätigkeit in Bewegung bringen, diese zu vergleichen, sie zu verknüpfen oder zu trennen, und so den rohen Stoff sinnlicher Eindrücke zu einer Erkenntnis der Gegenstände zu verarbeiten, die Erfahrung heißt?“ (highlighted by Psilojannopoulos 2013, p. 38).Needless to say, this is only circumstantial evidence for Thomasius’ influence on Kant.

23 Moreover, the similarities between Kant and Thomasius are not only present in their theoretical philosophy but also in their practical philosophy. Thomasius, following the Pietistic tradition, describes peace as mankind’s supreme moral achievement and the honestum as the man who follows the principle according to which everyone must behave and act in accordance with how he wishes others should behave in the same situation.

24 Kant was influenced directly by Darjes’s logical doctrine (Lorini 2011).

25 “[…] Schema illud perceptionum, de quo ante dixi, est solummodo nexus entium passiuorum atque actiouorum.”

26 “[…] puisqu’il est certain que notre imagination est d’un grand secours pour la mémoire, on ne peut pas absolument rejeter la méthode des schématismes, pourvu que les images n’ayant rien d’extravagant ni de puérile, & qu’on ne les applique pas à des choses qui n’en sont point du tout susceptibles.”

27 “Docet experientia, et evincit ratio, corpora organisata esse ex se et sua natura transmutabilia in alios schematismos.”

28 Tetens’s Philosophische Versuche, was in Kant’s library (Warda 1922). Although Kant does not mention Tetens in his main works (only once in the whole Critique), he does so in his letters to Marcus Herz from April 1778 and May 1782 and to Christian Garve from August 1783 (AA X, p. 232 and p. 270) and notes R 4847 and R 4848 (AA XVIII, p. 5). Cf. Kuhen 1989, pp. 365–366. The evaluation of Tetens’s inquiry as being subjective is well-known: R 4901 (AA XVIII, p. 23). Tetens’s inquiry is subjective insofar as it concerns human faculties and their relation in general and not as faculties involved in cognition intended to be objective. Kant’s interest is directed not to the description of human cognition, but to the understanding and justification of the objectivity of epistemic judgements. (Cf. Carl 1989, pp. 119–126).

29 Hamann 1959, p. 81.

30 However, this reference might be misleading. Although Tetens gives great importance to observation and physiological inquiries, it is important to remember his criticism of Hume’s discussion of causal relation and his account concerning the possibility of metaphysics. Cf. Kuhen 1989, pp. 368–72.

31 The expression ‘schema perceptionis’ is used also by Justus Christian Hennings to refer to the capacity to have representations and perceptions: “Tale vero non spontaneum, quod nexu plurium entium simplicium constituitur, cuius ioe motus modificaru possunt, vt enti spontaneo occasionem cogitandi prahere queant, vocatur SCHEMA REPRAESENTATIONIS s. Perceptionis. Ergo schema perceptionis quando necessarium sit, hinc colligere datur” (Hennings 1768, p. 154.)

32 “Zu jedweder Seelenäußerung wirket ein gewisser innerer Theil unsers Körpers bey; wir mögen diesen Theil das Gehirn, das sensorium commune, Seelenorgan, schema perceptionis, oder wie wir wollen, benennen.”

33 “Les idées ne sont revetues que de signes naturels, et ces signes sont les images que les Objets tracent dans le Cerveau.”

34 “[…] le Siege de l’Ame est une petite Machine prodigieusement composée et pourtant fort simple dans sa composition. […] On peut se représenter cet admirable Instrument des opérations de nostre Ame sous l’image d’un Clavecin, d’une Orgue, d’une Horloge ou sous celle de quelque autre Machine beaucoup plus composée encore. […] L’Âme est le Musicien qui exécute sur cette Machine différents airs ou qui juge de ceux qui y sont exécutés et qui les répète.”

35 “Die Seele empfindet, sie hat Vorstellungen von Sachen, von Beschaffenheiten und Verhältnissen, und sie denkt.”

36 “Was denn Fühlen oder Empfinden sey? Da gestehe ich sogleich mein Unvermögen, es erklären zu können. Es ist eine einfache Seelenäußerung, die ich nicht in noch feinere zu zerfasern weiß.”

37 “Was unmittelbar gefühlt wird, ist allezeit, wo sich diese Äußerung unserer Seele beobachten lässt, etwas leidentliches, eine passive Modifikation der Seele […] Es ist niemals die Thätigkeit selbst, nie das Bestreben selbst, welches wir unmittelbar fühlen; es ist eine bleibende Folge von etwas, das von unserer selbsttätigen Kraft nun nicht hervorgebracht wird, sondern schon hervorgebracht worden ist, wenn es ein Objekt des Gefühls ist;”

38 “[…] es sind Vorstellungen von andern Gegenständen; Modifikationen, die etwas anders abbilden, und, wenn sie gegenwärtig sind, nicht sowohl sich selbst, als ihre Gegenstände uns sehen und erkennen lassen.”

39 “Aus den Vorstellungen werden Ideen und Gedanken. Für sich sind sie dieß nicht. Das Bild von dem Mond ist nur die Materie zu der Idee von dem Mond. Es fehlt ihm noch die Form: die Jdee enthält außer der Vorstellung ein Bewußtsein, ein Gewahrnehmen und Unterscheiden, und setzet Vergleichungen voraus, und Urtheile, sobald wir sie als eine Idee von einem gewissen Gegenstand ansehen.”

40 “[…] la fonction reproductive est […] examinée dans sa constitution et dans son exercice psychologique, et se distingue de la manière dont Kant l’avait traitée surtout par l’absence de toute allusion à un pouvoir synthétique quelconque.”

41 “[…] die Idee oder Vorstellung von meinem Ich, keine Sammlung von einzeln Vorstellungen sey, welche etwan die Einbildungskraft zu einem Ganzen gemacht hat, wie sie die einzelnen Vorstellungen von Soldaten zu einer Vorstellung von Einem Regiment vereinigt. Jene Vereinigung liegt in der Empfindung selbst, in der Natur, nicht in einer selbst gemachten Verbindung. Daher entsteht eine Vorstellung von Einem Subjekt mit verschiedenen Beschaffenheiten, das heißt, die aus der Empfindung unmittelbar entstehende Vorstellung muß so gedacht, und zu einer solchen Idee gemacht werden, wozu der gemeine Menschenverstand sie wirklich machet, der nur dann diese Idee auf Humisch gebildet haben konnte, wenn er in seiner natürlichen Beobachtung eben so viel bei ihr übersehen, und nur an Einer sich aufnehmenden Seite sie gefasst hatte, als dieser feine Metaphysiker bei seiner Spekulation, da er jeden Zug nach dem andern deutlich ablösen wollte.”

42 “[…] in dem menschlichen Seelenwesen außerdem körperlichen Organ, ein einfaches unkörperliches Weſen, eine wahre substantielle Einheit vorhanden sey, welche eigentlich das fühlende, denkende und wollende Ding ist”.

43 “[…] zu jedweder Seelenäußerung wirkt ein gewisser innerer Theil unsers Körpers bey; wir mögen diesen Theil das Gehirn, das sensorium commune, Seelenorgan, schema perceptionis, oder wie wir wollen, benennen. Die andere Grundwahrheit ist folgende: “Es gibt außer den gedachten körperlichen Seelenorganen in uns ein Wesen, das zwar in Vereinigung mit jenen wirkt, aber für sich ein eigenes bestehendes Ding oder eine Substanz ist, die wir die Seele in psychologischer Bedeutung oder unser Ich nennen.”

44 On the notion of self in Tetens see Thiel 2018, pp. 59–75.

45 “Die Physiologie und Psychologie hat nunmehr so viele Fakta gesammelt, welche diese durchgängige Mitveränderung des Gehirns zu allen Seelenveränderungen offenbar machen, daß solche als außer Zweifel gesetzt angesehen werden kann.”

46 Among the above-mentioned philosophers, Kant has direct knowledge of the works of Wolff, D’Alembert, Darjes and Tetens (Warda 1922).