What is rhetorical invention?

John Quincy Adams, answered from the texts and cited to the page.

John Quincy Adams answers

Invention is the discovery, by thought, of the things best adapted to obtain the purpose of the speaker.¹ That is the whole of it in a sentence; but the sentence conceals a great deal. Your first concern, whenever you are called upon to speak in public upon any formal occasion, is what you are to say — what the reflections of your mind can suggest to you, suitable to your subject.²

That first conception of the thoughts is what exercises invention, and it is therefore the first chapter in the book of rhetoric, prior to disposition (the arrangement of what invention has supplied), prior to elocution, prior to everything.³ Aristotle appears to have been the first to work out the principal subdivision under this article, and his test was drawn from the nature of the purposes to which oratorical discourse is applied.⁴

He observed that all public speaking has an object of reference either to past, present, or future time, and with a view to something to be done or omitted — which gives you deliberative eloquence for the assembly, forensic for the courts, and the third kind, demonstrative, for occasions of praise or blame.⁵ The distinction matters for invention because the questions a speaker must find arguments for differ by kind: the deliberative speaker asks what shall be done; the forensic speaker asks what was done; and the materials of persuasion appropriate to each are not interchangeable.

One further point worth holding clearly: invention tells you where to collect the materials of persuasion, but it does not yet tell you in what form to produce them, or in what order to marshal them to greatest advantage — that is the work of the proof, of confirmation and confutation, which comes later and to which everything else is subservient.⁶ Invention is the quarry; the building is still to be done.

Sources

1. Invention then is the discovery, by thought, of the things best adapted to obtain the purpose of the speaker; and one of the objects of the rhetorician is to indicate to the practical orator the means of sharpening this faculty, and of facilitating its exercise.

   Lectures on Rhetoric and Oratory, Vol 1

2. your first concern will be, what you are to say; what the reflections of your mind can suggest to you, suitable to your subject. This first conception of the thoughts will exercise your invention.

   Lectures on Rhetoric and Oratory, Vol 1

3. Invention therefore is the first chapter in the book of rhetoric. Your next step will be to arrange the thoughts, which your invention has supplied; and this will be disposition.

   Lectures on Rhetoric and Oratory, Vol 1

4. To this end Aristotle appears to have been the first inventor of the principal subdivision under this article; and the test of his distinction was drawn from the nature of the purposes, to which the oratorical discourses of that age were applied.

   Lectures on Rhetoric and Oratory, Vol 1

5. He considered, that all public speaking had an object of reference either to past, present, or future time; and with a view to something to be done or omitted. That all such questions must necessarily be subjects of deliberation; and he accordingly called them deliberative discourses. That those, which referred to time past, consisted of controversies in the courts of law, respecting rights previously existing, or wrongs previously committed.

   Lectures on Rhetoric and Oratory, Vol 1

6. My present purpose is to indicate not where these materials of persuasion are to be collected, but the various forms, in which they may be produced, and the order in which they may to the greatest advantage be marshalled.

   Lectures on Rhetoric and Oratory, Vol 2