The Free Radical Online - Perigo vs. Nola

Round Two: Robert Nola Responds

I wish to take up a point in Lindsay Perigo's reply to my reply (TFR #31) and then make a general observation.

I said that logic does not concern itself with whether or not the premises are true or false; we can validly argue from the false as well as the true. And the certification of the validity of rules of logic is not done by an appeal to reality. But of course we all have an interest in sound argument in which not only is the argument valid but its premises are true; but this is a matter outside the scope of valid reasoning itself.

But Mr Perigo insists: 'Logic, in the Objectivist view, does not permit false premises to begin with!'. NOT PERMIT! Perigo-style Objectivists might want to act as a kind of thought police for admissible premises. But this is not the view of his Gurus Aristotle and Rand.

Aristotle was well aware in his logical treatises that we can reason validly from false premises. He also discusses an important case of this, called reductio ad impossibile. This inference is common in mathematics and goes like this. Suppose you wish to prove P. Then assume the opposite, not-P, and derive (within the system) a contradiction from that assumption, Q and not-Q; then, infer as conclusion P. This form of argument contains false premises, not-P, and an interim conclusion as a further premise for the conclusion which is self-contradictory (and so false). If the Perigo Objectivist Thought Police were to ban these steps within a reductio argument, then much of mathematics would have to be abandoned!

Given that truth is the goal of inquiry, we might still have to argue against many a false claim on the way. In science we commonly attempt to assess a group of rival hypotheses not all of which can be true (and perhaps all of which are false). We reason about them to obtain their consequences which we then compare with what we can observe in an attempt to discover which, if any, is true. This employs both deductive and inductive reasoning. But the Perigo Objectivist Thought Police would not let us even reason about these rival hypotheses because some, or all, might be false!

Ayn Rand herself wrestled with this matter, and even though her arguments are murky and inconclusive she does comes out on the right side. In Objectivist Epistemology (p 301-4) she is asked whether if we deduce true predictions from a hypothesis we can infer that the hypothesis is true. To so infer is to commit the deductive Fallacy of Affirming the Consequent — though Rand does not clearly point this out. In the end she decides that this is part of the old problem of induction which she declines to discuss further saying that she has not worked on it. But others have long investigated what Objectivist Gurus have failed to (Aristotle included)!

The answer is simple. Given a true conclusion we cannot infer whether an hypothesis as premise is true or false; it could be either. What is important is the confirmatory support true predictions give hypotheses. And this is Hume's problem of induction. But Objectivists have in their lexicon a dismissive epithet for Hume — 'Subjectivist!'

During the Cultural Revolution in China the Red Guards dragged out and criticised those philosophy teachers who were influenced by Western doctrines for teaching, amongst other things, that deductive logic allows premises to be false. For them Mao's and Lenin's dialectical logic was superior because it enabled them to deal with reality directly.

Marxist dialectical logic is not the same as Objectivist logic, but both claim an exclusive purchase on reality. Unfortunately, advocates of both "logics" have the same features — they are cult members equipped with abusive epithets for opponents such as either 'revisionist' and 'capitalist dog', or 'subjectivist' and 'supporter of the nonsensical analytic/synthetic dichotomy'. (What kind of abuse is the last! Readers might like to know that the Objectivist bete noire, the subjectivist Kant, peddled that dichotomy!)

If Objectivists were to really study their Guru Aristotle then they might learn a little logic — but even a logic of possibility, contingency and necessity founded by Aristotle is (falsely) dismissed by Perigo because it is about the non-existent. Objectivists should note that the subject has moved on over the centuries from Aristotle's brilliant but narrow beginning.

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