Video from Thomistic Institute
"The calling of St. Thomas Aquinas was to pose all the most relevant questions, face all the most relevant difficulties involved in each question, and draw all the relevant distinctions. Argument and Dialectic (Aquinas 101) - Fr. James Brent, O.P." from video introduction.
"Now reasoning is an argument in which, certain things being laid down, something other than these necessarily comes about through them. (a) It is a 'demonstration', when the premisses from which the reasoning starts are true and primary, or are such that our knowledge of them has originally come through premisses which are primary and true: (b) reasoning, on the other hand, is 'dialectical', if it reasons from opinions that are generally accepted. Things are 'true' and 'primary' which are believed on the strength not of anything else but of themselves: for in regard to the first principles of science it is improper to ask any further for the why and wherefore of them; each of the first principles should command belief in and by itself. On the other hand, those opinions are 'generally accepted' which are accepted by every one or by the majority or by the philosophers-i.e. by all, or by the majority, or by the most notable and illustrious of them...from the website: Thomistic Institute Selection from Aristotle, trans. W. A. Pickard-Cambridge, Topica Bk 1, Pt. 1, in The Basic Works of Aristotle, ed. Richard McKeon (New York: The Modern Library, 2001).