From the responses of some rather earnest men to my last post I gather that I haven’t supplied substantive critiques of Molyneux to everyone’s fullest satisfaction.
In my review, I linked to Cian Chartier’s review, which pretty much covers the problems in Molyneux’s ‘logic’ (it also has a link to another review that deals with Molyneux’s political philosophy). But the link was buried in my text. Molyneux’s readers might find it below.
On Molyneux’s ‘logic’, I’ll just make a general point. Molyneux does abuse a sort of formal logic in attempting to explain valid reasoning, namely the syllogistic. At least, his paradigm for a valid argument is the textbook Sortes mortalis syllogism. And his initial example of “bad deductive reasoning” is a vicious syllogism:
- All plumbers can swim.
- Bob knows how to swim.
- Therefore Bob is a plumber.
He then goes on to draw equivalences between this vicious syllogism and valid syllogisms with false premises. Some logic people have complained of this as a confusion, though in fairness his vicious syllogism also contains one highly questionable premise. I find Molyneux’s prose too loose and hokey to pin him down to any specific confusion.
What is clear is this. If you’re going to give syllogisms as examples of good and bad reasoning, and you’re trying to teach people the difference, then you owe the reader an explanation of what makes a syllogism formally valid or invalid. Molyneux doesn’t explain this — almost certainly because he doesn’t know.
It would be unrealistic to expect him to explain that the above syllogism is in the second figure with no negative premise. But there are easier ways to understand syllogistic validity than by knowing all twenty-four valid moods. Venn diagrams, Carroll trees, any sort of decision method would have got the elementary point across, if Molyneux had grasped the elementary point.
You might think that syllogistic validity is too obvious to need explanation. But this is an illusion fostered by Molyneux’s not daring to venture far beyond the first figure. Try some of Lewis Carroll’s puzzles.
Since his discussion of syllogisms can’t help to enhance our informal understanding of validity, since, in fact, it is apt only to confuse readers who aren’t familiar with syllogisms, why did he invoke the syllogistic at all? As anyone who knows any logic knows, syllogistic is problematic as a model of informal reasoning. I wrote something on this. A limited formal model of validity is better than none, you might argue. But Molyneux doesn’t give any formal model; he just provides instances and says nothing about their form.
At the risk of encouraging my readers to commit the fallacy of affirming the consequent, note that this is exactly what you’d expect from a political propagandist who hopes to impress people with half-digested morsels from the unearthly table of ‘critical thinking’ guides in the Ayn Rand blogosphere.