“When they ardently desire of Victory, for the Sake of the Praise attending it, they will begin to feel the want, and be sensible of the use of the Use of Logic, or the Art of Reasoning to discover Truth, and of Arguing to defend it, and convince adversaries.”

Proposals Relating to the Education of Youth in Pensilvania (1749), p. 22 http://dewey.library.upenn.edu/sceti/printedbooksNew/index.cfm?textID=franklin_youth&PagePosition=1; the statement relates to the teaching of History as a subject, and the last quoted paragraph concludes with the footnote "†": Public Disputes warm the Imagination, whet the Industry, and strengthen the natural Abilities.
Context: History will also afford frequent Opportunities of showing the Necessity of a Publick Religion, from its Usefulness to the Publick; the Advantage of a Religious Character among private Persons; the Mischiefs of Superstition, &c. and the Excellency of the above all others antient or modern.
History will also give Occasion to expatiate on the advantage of Civil Orders and Constitutions, how men and their properties are protected by joining in Societies and establishing Government; their Industry encouraged and rewarded, Arts invented, and Life made more comfortable: the Advantages of Liberty, Mischiefs of Licentiousness, Benefits arising from good Laws and a due Execution of Justice &c. Thus may the first Principles of sound Politics be fixed in the minds of youth.
On Historical occasions, Questions of Right and Wrong, Justice and Injustice, will naturally arise, and may be put to Youth, which they may debate in Conversation and in Writing. When they ardently desire of Victory, for the Sake of the Praise attending it, they will begin to feel the want, and be sensible of the use of the Use of Logic, or the Art of Reasoning to discover Truth, and of Arguing to defend it, and convince adversaries.