At the end of his book, Gerson quotes with approval Francis Cornford's assessment, that the theory of Forms and the immortality of the soul are the "twin pillars of Platonism." Gerson comments:
I think Cornford's observation is essentially correct and important, though we have seen reason neither to speak of 'the' theory of Forms nor to identify Plato's views about Forms simply with what is said in the so-called middle dialogues. In addition, we ahve also seen reason to deny that the immortality of the soul is personal immortality in the sense that it is typically and uncritically conceived of within many religions. With the appropriate qualifications made, I think it is fair to conclude that the "twin pillars" also support Aristotle's Platonism (289).How so? According to Gerson, Aristotle is a Platonist as regards the existence of Forms, because he believes in "intelligibles", objects of thought, which exist in the mind of God; he is a Platonist as regards the immortality of the soul, because he holds that there is an aspect of the human soul which is immaterial and survives the destruction of the body, and also that, in ethics, we should strive to identify ourselves with this part of us.
Let us grant that Gerson is correct, that Aristotle, in his mature and settled thoughts, held such things. (And I believe Gerson is correct about this.) Still, does that make him a Platonist? We may agree that Aristotle would not be the sort of 'empiricist' that Jaeger and others have taken him to be--and, in particular, he would not be a 'naturalist'. But presumably the philosophical universe consists of more viewpoints than Platonism and empiricism.
I think this is where Gerson's claim at the very end of his book, that Aristotle is a Platonist malgré lui, begins to acquire some force. In saying this Gerson means:
...perhaps Aristotle could not adhere to the doctrines that he incontestably adheres to were he not thereby committed to principles that are in harmony with Platonism. ... [perhaps] an authentic Aristotelian, if he be consistent, is inevitably embracing a philosophical position that is in harmony with Platonism. That is, there cannot be an authentic form of Aristotelianism that is not in harmony with Platonism ... (274).The point may I think be put in the following way. Aristotle is committed to such doctrines as the immortality of the soul and the reality of objects of thought in the Divine Mind. He says, however, very little about such things: he gives no account of the significance of the continued existence of the human soul, and he says little about how objects of thought in the Divine Mind play a role in God's working as a first cause. Yet any attempt to spell out such things would inevitably rely upon some broadly Platonist framework, or would tend to bring Aristotle into fairly close alignment with Plato.
In justice (this line of thought continues) we cannot remove these elements from Aristotle's philosophy, yet neither can we image that they should be left just as they are found in the Aristotelian corpus--that is, as obscure and undeveloped suggestions. They are too important for that. But then attempt to give due emphasis to these features, and one will be led to something that, on any fair appreciation, will count as a variant of Platonism.
I think this is Gerson's best argument. It is not that Aristotelianism as found in the corpus is a variant of Platonism, but that what is found in the corpus cries out for development and systematization, but there appears to be no way in which that could be done except within some broadly Platonic framework.