An alleged fallacy
I’ve been enjoying Part One (“Ancient Philosophy”) of Anthony Kenny’s four-part New History of Philosophy. The selection and arrangement of themes is pretty tidy, and in one passage – the conclusion of the epistemological chapter – it’s almost breathtaking how the dominoes topple over.
The study of ancient epistemology can teach us much about the nature of knowledge and the limits of scepticism. Several insights became part of the patrimony of all future philosophy: knowledge can only be of what is true; knowledge is only knowledge if it can appeal implicitly or explicitly to some kind of support, whether from experience, reasoning, or some other source; and one who claims knowledge must be resolute, excluding the possibility of being rightly converted, at a later stage, to a different view.If Plato, Aristotle, the Epicureans, the Stoics, and (presumably, for centuries) their descendents all really were confused on this point, then: Oof.
However, ancient epistemology is bedevilled by two different but related fallacies. Both of them are generated by a misunderstanding of the truth that whatever is knowledge must be true. One of the fallacies haunts classical epistemology, up to the time of Aristotle; the other fallacy haunts Hellenistic and imperial epistemology.
The first fallacy is this. “Whatever is knowledge must be true” may be interpreted in two ways:
(1) Necessarily, if p is known, p is true
or
(2) If p is known, p is necessarily true.
(1) is true but (2) is false. It is a necessary truth that if I know you are sitting down, then you are sitting down; but if I know you are sitting down it is not a necessary truth that you are sitting down; you may get up at any moment. Plato and Aristotle, over and over again, seem to regard (2) as indistinguishable from (1). Given the necessary connection between knowledge and truth, they seem to think, only what is necessary can be known. From the acceptance of (2) there flows the construction of the theory of eternal and immutable Ideas, and there flows the impossible ideal of Aristotelian science.
If whatever is knowledge must be true, then it may seem that knowledge must be the exercise of a faculty that cannot err. This is the form that the fallacy takes in Hellenistic times. The Epicureans and Stoics, unlike Plato and Aristotle, are prepared to countenance knowledge not just of eternal truths, but of mundane contingencies such as that Dion is now walking. But this, they claim, is possible only if we have faculties – whether sense or reason – that are capable of infallible operation. The Hellenistic fallacy is just the mirror image of the classical fallacy. Let F stand for some faculty. Then it is true that
It is impossible, if F knows that p, that F has gone wrong.
But that is not the same as, nor is it true that,
If F knows that p, then it was impossible for F to go wrong.
The epistemological fallacy, both in its classical and in its Hellenistic form, would cast long shadows through philosophy’s history.