Theory of Forms
The full Greek text of Alexander's commentary which includes "On Ideas" is published in the first volume of the "Commentaria in Aristotelem Graeca". Excerpts from this, along with an English translation and commentary by Gail Fine, are available in "On Ideas: Aristotle's Criticism of Plato's Theory of Forms" published by the Oxford University Press in 1993. This translation is also reproduced with notes in "Aristotle: Selections", edited by Terence Irwin and Gail Fine and published by Hackett Publishing in 1995.