Full Idea
There are many men that reason exceeding clear and rightly, who know not how to make a syllogism
Gist of Idea
Many people can reason well, yet can't make a syllogism
Source
John Locke (Essay Conc Human Understanding (2nd Ed) [1694], 4.17.04)
Book Reference
Locke,John: 'Essay Concerning Human Understanding', ed/tr. Nidditch,P.H. [OUP 1979], p.670
A Reaction
On the one hand this is just Locke's scepticism about the whole business of Aristotelian logic, but on the other hand it may be a perspicuous observation that logical thought extends far beyond what was catalogued by Aristotle.