From The Oxford English Dictionary:
protreptic, n. and adj.
. . . .
A book, writing, or speech intended to exhort or instruct; an exhortation, an instruction.
. . . .
1678 R. Cudworth True Intellect. Syst. Universe i. iii. 125 To rank Anaximander, amongst the Divine Philosophers, as he [sc.Clement] doth in his Protreptick to the Greeks.
1797 T. Beddoes Alternatives Compared 9 He has this time so compounded his protreptic, as to destroy its intoxicating effect.
Link to the rest at The Oxford English Dictionary
Ahhh! So protreptic is the flip side to polemic.
Cool! Two words in one post. I’d forgotten what polemic means.