Читать книгу The Philosopher's Toolkit - Julian Baggini, Julian Baggini - Страница 37

Another way of understanding how arguments work as to think of them along the model of sausage machines. You put ingredients (premises) in, and then you get something (conclusions) out. Deductive arguments may be thought of as the best kind of sausage machine because they guarantee their output in the sense that when you put in entirely good ingredients (all true premises), you get out a fine‐quality product (true conclusions). Of course, if you don’t start with good ingredients, deductive arguments don’t guarantee a good end product.

Invalid arguments are not generally desirable machines to employ. They provide no guarantee whatsoever for the quality of the end product. You might put in good ingredients (true premises) and sometimes get a high‐quality result (a true conclusion). Other times good ingredients might yield a frustratingly poor result (a false conclusion).

Stranger still (and very different from sausage machines), with invalid deductive arguments you might sometimes put in poor ingredients (one or more false premises) but actually end up with a good result (a true conclusion). Of course, in other cases with invalid machines you put in poor ingredients and end up with rubbish. The thing about invalid machines is that you don’t know what you’ll get out. With valid machines, when you put in good ingredients (though only when you put in good ingredients), you have assurance. In sum:

Invalid argument

 Put in false premise(s) → get out either a true or false conclusion

 Put in true premise(s) → get out either a true or false conclusion

Valid argument

 Put in false premise(s) → get out either a true or false conclusion

 Put in true premise(s) → get out always and only a true conclusion