Full Idea
The Platonists, on the basis of purely logical arguments, posit the existence of an indivisible 'triangle in itself'.
Gist of Idea
Platonists argue for the indivisible triangle-in-itself
Source
report of Plato (works [c.375 BCE]) by Aristotle - Coming-to-be and Passing-away (Gen/Corr) 316a15
Book Reference
Democritus: 'Early Greek Phil VII: Democritus', ed/tr. Laks,A/Most,G [Harvard Loeb 2016], p.103
A Reaction
A helpful confirmation that geometrical figures really are among the Forms (bearing in mind that numbers are not, because they contain one another). What shape is the Form of the triangle?