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^1.42 Think about your two books, Your Book of Beliefs and Your Book of Justified Beliefs. The Supporting Justified Belief Rule tells us that a belief in the first book, B1, earns a place in the second iff it's supported by other beliefs that have a place in the second book. If we adhere to this rule and there's a finite (but non‐zero) number of entries in Your Book of Justified Beliefs, infinitism must be mistaken. Let's now consider an alternative to infinitism, coherentism.

^1.43 Imagine that you have Your Book of Beliefs in hand. A team of epistemologists has promised to send you a copy of Your Book of Justified Beliefs once they finish a thorough investigation of you, your beliefs, and your belief‐forming habits. Curiosity gets the better of you, so you start to wonder which entries in your book will be entries in theirs. The Supporting Justified Belief Rule tells you this much: if any of your beliefs is included in both books, it's because there's something in both books that supports it. You start to look for connections between the entries. You discover that you can group the entries into categories like this:

 Entries that fit with a significant number of other entries and do not conflict with any other entries.

 Entries that conflict with other entries and are not supported by a significant number of entries.

 Entries that neither conflict with other entries nor fit with other entries.

 Entries that fit with a significant number of other entries but also conflict with other entries.

According to the Supporting Justified Belief Rule, the entries that fit into the second and third categories won't be justified. You won't expect to find these entries in Your Book of Justified Beliefs. The fourth category is tricky. On the one hand, some of these entries might receive strong support from other entries and so you might think that the conflict doesn't really threaten them. Some of these entries might receive weak support and look bad in light of well‐supported entries. Let's set these aside for the time being.

^1.44 The best candidates for entries in Your Book of Justified Beliefs will be those in the first group – viz. entries that fit with a significant number of other entries and do not conflict with any other entries. Question: could it be that all it takes for a belief to be justified is for it to fit into the first category? Could mutual support between beliefs be all that's required for these beliefs to be justified? This is indeed what the coherentist thinks. As Catherine Z. Elgin (1996) states the idea, beliefs that are justified are parts of a system where the parts are “reasonable in light of one another” (1996, p. 13).

^1.45 There is are two key components to this core idea: (i) items that aren't contained in Your Book of Beliefs simply won't have a direct bearing on whether beliefs that belong to a coherent system are really justified or not; and, second, (ii) justified beliefs are justified because of their place in a system of mutually supporting items. Instead of thinking of your justified beliefs as forming a structure like a tower or pyramid with foundational beliefs at the bottom and inferential beliefs at the top, think about your system of justified beliefs as forming a piece of woven cloth. The strength of a piece of woven fabric has all to do with the interlocking warp and weft strings. It doesn't require any unsupported supporters.

^1.46 As you examine your beliefs, you might find that some beliefs aren't supported by any further beliefs. These beliefs, according to the coherentist, lack the kind of support required for justified beliefs. There is not some other source of rational support that isn't some further belief. As Donald Davidson remarked, “nothing can count as a reason for holding a belief except another belief” (1986, p. 141). The coherentist will say that there are various causes of our beliefs (e.g. experiences, sensations, apparent memories, etc.), but will insist that it's just relations between beliefs that determine whether they're justified.²⁹

^1.47 Even the critics of coherentism will acknowledge that there are cases where coherence seems to play an important role in the justification of our beliefs, but the crucial question isn't whether the overall coherence of a system of beliefs plays some role in the justification of belief, but whether the justification of our beliefs could be wholly determined by the coherence of the system. Coherentists like to think of justified beliefs as part of a web of belief that has a sufficiently high degree of coherence, in part because we cannot divide the parts of a web into parts, isolating the foundations and distinguishing them from the superstructure. In a web, every part is supported by the other parts, and every part lends its support to the structure as a whole.

^1.48 Unsurprisingly, coherentism's critics object to the view on the grounds that it fails to recognize the role that things external to the web of belief play in the justification of the beliefs that constitute the web. The coherentist doesn't look at all beyond the web of belief for further support that would justify the beliefs bound up in the web. But shouldn't she do so?

^1.49 If coherentists wants to convince us that our justified beliefs are justified because they cohere with each other, they need to show that the beliefs that provide rational support for our beliefs derive their justification exclusively from further beliefs, and not from anything located outside the circle of belief. If they don't, there will always be that nagging feeling that some of the justificatory work is done by intuition, experience, testimony, or something outside the circle of belief.

^1.50 An example should help to make this worry vivid. Imagine we are playing a game in which your friend places something on a platter, covers it with a silver cloche, and lifts the cloche with a flourish so that you can see what's on the platter. Before your friend lifts the silver cloche, you have no beliefs at all about what's on the silver platter. (For all you know, it could be anything small enough to fit under a cloche, from a battery to a coin to a piece of cheese.) After the reveal, everything changed – there's a tomato! You quickly came to believe that the thing on the platter was a tomato. Let's suppose that that's all you came to believe and let's suppose that you didn't just believe that the thing on the platter was a tomato. Let's suppose that you knew that it was and so justifiably believed that it was.

^1.51 If this is a plausible description of what happens, we have the makings of a good objection to coherentism:

Isolation Objection

P1.The belief that the object is a tomato couldn't be justified before the reveal.

P2. The belief that the object is a tomato could be justified after the reveal.

P3. difference in justification is a normative difference.

P4. If there is a normative difference between beliefs formed before and after the reveal, there must be some further difference between the beliefs that accounts for this normative difference.

C1. There must be some further difference between the beliefs formed before and after the reveal that accounts for this difference in justification before and after the reveal.

P5.According to the coherentist, the only difference between beliefs that could account for a difference in justification is how well they cohere with the rest of the believer's beliefs.

P6.The belief that the object is a tomato coheres with the rest of the subject's beliefs equally well before the reveal and after it.

C2.Thus, if coherentism is true, then there is no difference between the beliefs formed before and after the reveal that could account for the relevant difference in justification before and after the reveal.

The crucial point is this. Prior to the reveal, the belief that the object is a tomato wasn't supported by other beliefs. (You might have had good reason to think something would be under the cloche, but you didn't have good enough reason to believe that it was a tomato, a fruit, something red, etc.) When the tomato was revealed, there was a short time when your beliefs stayed the same but your experiences changed. It's only when there's a difference in your experience that we think that you're in a position to justifiably judge that the object is a tomato. It's worth emphasizing that what changes here and seems to account for the fact that you are now in a good position to judge that it's a tomato on the plate is your experience, not your beliefs. Thus, while it might seem to you that something of great significance changed when your experience changed, there's nothing that the coherentist can appeal to in trying to explain why it's a consequence of the reveal and the experience of the tomato that you can now justifiably judge the object to be a tomato.

^1.52 Might the preceding line of objection against the coherentist be too quick? Here's a natural line of response. In setting up the example, you've been asked to imagine that only one new belief is formed as a consequence of the great reveal. But perhaps that is psychologically implausible. Wouldn't we expect subjects to form an additional belief, such as the belief that the thing on the plate looks like a tomato?³⁰ If we have two beliefs here, couldn't the coherentist say that these two beliefs are mutually supporting? Couldn't she say that the belief that the thing is a tomato supports the belief that it looks like a tomato, and that the belief that it looks like a tomato is something that supports the belief that it is a tomato? If she said that, she could say that there is something that changes after the great reveal. Before that, she didn't have any belief that supported her belief that the thing is the tomato. After that, however, she did. She formed the beliefs that the thing is a tomato and that it looks like one concurrently, and each supports the other.

^1.53 But even if the coherentists said this, it wouldn't get them out of the jam. Suppose that you were playing this game with a friend. Upon seeing the tomato, you spontaneously formed these (allegedly) mutually supporting beliefs:

1 This looks like a tomato. This is a tomato.

^1.54 Your friend, let's suppose, formed these beliefs:

1 This looks like a lemon. This is a lemon.

^1.55 Now, we're not supposing that your friend suffered from some sort of illusion or hallucination. They had an experience indistinguishable from yours. We're not supposing that they're confused about how tomatoes and lemons look. We're also not supposing that you've shared your answers yet. You spontaneously judge that the beliefs in (1) are correct, and your friend spontaneously judges that the beliefs in (2) are correct. It's surely possible for one's beliefs to fail to “match” one's experience and for one to fail to notice this. Suppose that such a mistake is what happened in the case of your friend's assessment of the fruit in plain view.

^1.56 Yours and your friend's sets of beliefs are equally coherent. Thus, from the perspective of coherentism, there are no grounds for saying that your beliefs are better justified than your friend's beliefs. And yet it seems that there's a clear difference between your beliefs, and that your beliefs are better justified than theirs. This is a different normative difference from the one we started with, and it doesn't look like the coherentist can account for this difference.

^1.57 It seems that the coherentist's fixation on the internal relations between beliefs leads them to overlook the rational significance of mental factors external to belief (e.g. relations between beliefs and experiences). Moreover, it seems that a natural story about how the beliefs in (1) are justified is one that adverts to experience. Your beliefs are justified and your friend's beliefs are not because your beliefs fit your experiences and theirs do not. This difference is not a difference in terms of how coherent your beliefs are. This factor plays no role in filling the pages of Your Book of Beliefs, but this just seems to be an indication that there's more to the explanation as to how your beliefs are justified than what's contained in that book. Perhaps we cannot really tell which of your beliefs belong to the book of Your Justified Beliefs until we know something about your experiences and how they fit with your experiences.

^1.58 We didn't need perceptual beliefs to make the point. The point could have been made equally well using introspective beliefs, the beliefs you form straight off about your own mental life. And, indeed, such an introspective example is offered by Ernest Sosa, in his famous paper “The Raft and the Pyramid” (1980). Consider this passage, in which Sosa poses the following thought experiment:

Thus take my belief that I have a headache when I do have a splitting headache, and let us suppose that this does cohere within my present body of beliefs … such a belief may well have relevant relations of explanation, logic, or probability with at most a small set of other beliefs of mine at the time: say, that I am not free of headache, that I am in pain, that someone is in pain, and the like. If so, then an equally coherent alternative is not far to seek. Let everything remain constant, including the splitting headache, except for the following: replace the belief that I have a headache with the belief that I do not have a headache, the belief that I am in pain with the belief that I am not in pain, the belief that someone is in pain with the belief that someone is not in pain, and so on. I contend that my resulting hypothetical system of beliefs would cohere as fully as does my actual system of beliefs, and yet my hypothetical belief that I do not have a headache would not therefore be justified. What makes this difference concerning justification between my actual belief that I have a headache and the hypothetical belief that I am free of headache, each as coherent as the other within its own system, if not the actual splitting headache? But the headache is not itself a belief nor a relation among beliefs and is thus in no way constitutive of the internal coherence of my body of beliefs. (1980, p. 19, italics added)

^1.59 Sosa's thought experiment offers reason to doubt that the justification for introspective beliefs such as that you have a headache right now derives from facts about how your beliefs are related to one another. This is all thse more reason to see why the Isolation Objection is a pressing one in light of the coherentist's claim that the only relevant difference between justified and unjustified beliefs is how well they cohere with the rest of the believer's beliefs.

^1.60 The intuition that underwrites the Isolation Objection is related to another influential objection to coherentism. Some of the clearest cases of irrational belief are cases in which someone is caught in the grips of delusion or subject to brainwashing. It doesn't matter whether our example involves a cult member brainwashed into believing that billions of years ago rational beings navigated the universe in spaceships that looked very similar to the cars of the 1950s or whether our example involves someone who firmly believes that their loved ones have been replaced by impostors.³¹ While the beliefs of such believers seem to be paradigmatic cases of irrational belief, it doesn't seem that we can account for the irrationality of such beliefs in terms of considerations of coherence. We want to say that our beliefs are rational, theirs are not, and that it's clear that there's a significant normative difference between them, but this difference cannot be traced to something like a degree of coherence that our beliefs display that theirs lack or the presence of incoherence that their beliefs display that ours do not. Part of what's so disturbing about subjects like this, subjects we'd describe as “having lost touch with reality,” is that their beliefs are often chillingly coherent. The most salient difference between our beliefs and theirs is that our beliefs are tethered to reality because they are properly responsive to new experiences. Unfortunately for the coherentists, they cannot straightforwardly accommodate this point, as they see justification as having all to do with relations between beliefs.³²