The Quaestiones in tertium De anima is a document typical of his first teaching. It gives the impression of a young professor (master) of 30 years, teaching at the Faculty of Arts, infatuated by philosophy, and not caring much for the religious implications of his theses. The primary doctrine concerns ‘‘the unity of the intellect,’’ inspired by the third book of Aristotle’s De anima. According to this literal interpretation, there exists only one ‘‘possible intellect’’ for the whole of humanity. What is this intellect? According to the doctrine of Aristotle, the intellect has a dual function. On the one hand, it is ‘‘active,’’ like a light that illuminates the sensible images in order to identify the intelligible core. This process of abstraction makes bare the essence of material things to render them compatible with the intellect. On the other hand, the intellect is ‘‘passive’’ in that it receives these intelligible abstract forms. It is this function that is called the ‘‘possible intellect.’’
However, according to Thomas Aquinas’ interpretation, for example, it is clearly the individual human being, Peter or Socrates, that is the subject of this intellect. It is not the intellect that thinks, but the human being, this human being of flesh and bones. According to Thomas, the intellective soul, its substantial form, is what constitutes the human being. For Siger, however, the intellect is completely separated from matter. Not only is it not material, as demonstrated by Aristotle, but it is apart from individual humans. The intellect is a separate and eternal substance, unique in species, genderless and incorruptible, therefore it cannot play the role of substantial form of the body. This is the thesis called “Averroistic” about the unity of the intellect, which Siger indeed reads in the Muslim thinker’s commentary of the books of Aristotle.
Is Siger really then this “independent spirit and vigorous thinker’’ that he has been described as? Or did he simply have second-hand knowledge of Averroes’ books? It is probably by reading Aquinas’ Commentary on the Sentences that Siger discovered the Averroist movement, which defends the separation and the unity of the possible intellect. Siger seems to have been content to unite several views without noticing the inconsistency of holding them simultaneously. We discover an author of limited culture, where lack of information does nothing to the faculty of invention. Once again, opinions differ.
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