Can we combine the results from the various case-studies into some more general conclusions about Galen’s views on human nature and the soul? First, I would like to repeat the same caveat that I have set out in the introduction. I have analysed a limited number of works by Galen, more in particular a number of works that are more philosophical than many others. Especially QAM and Galen’s interpretation of the Timaeus in various works, as well as the contested Larrain fragments, are more speculative than many other Galenic works, from which we might well derive quite a different picture of Galen. Therefore, the conclusions arrived at in each individual case-study must be read in the specific context of the selected key-texts.

On the other hand, we have seen that the concept of the soul and of human nature that Galen develops in QAM, HNH, and his work on the Timaeus, do show strong resemblances and an inner consistency that Galen also makes explicit through references. Also, we have seen that, although the views he works out in these works involve more philosophical speculation than Galen is comfortable with in some of his other works, these views are in important respects supported by works such as Hipp. Elem., Temp., Loc. Aff. and Nat. Fac. What does this mean, and how do we reconcile this consistency in content with the inconsistency with regard to Galen’s careful attitude in other works?

When we look at works in which Galen is willing to delve into the questions on human nature and the soul, we find that he develops what he characterizes as a plausible position. The plausibility of this position is, indeed, based on and derived from his findings in other works, such as those mentioned above, in which he generally refrains from delving into such more theoretical questions. The position comes down to an understanding of the human being as hylomorphic, constituted by the same two basic principles that constitute everything else, namely, a specific mixture of the four elemental qualities in a matter without quality as such. Since these qualities are primarily active and soul is a principle of movement, they are to be understood, in their specific interaction, as the primary cause of our activities and affections, i.e. as the substance of our soul. The specific mixtures that cause our activities and affections are located within the organs from which these are exercised, namely, the brain, heart and liver. With this notion of the substance of the soul as a bodily mixture, Galen makes use of the ambiguity of the term οὐσία and conflates the two senses of ‘what something essentially is’ and ‘the stuff of something’. What man essentially is, becomes the stuff in man that is primarily active, and that, therefore, functions as the cause of man’s activities and affections. This is how Galen’s concept of the nature of man and the substance of the soul of man are conflated.

Within this schema, the substance of the rational soul has an exceptional position, as we have seen both in our analysis of QAM as well as in our discussion of Galen’s interpretation of the Timaeus. It has a likeness to the heavenly bodies, which are divine and supremely intelligent, and it has, in some cases at least, the capacity to undertake a project of self-amelioration through alteration of its own substance. The ideal that Galen presents, is to liken the substance of one’s rational soul to the substance of the heavenly bodies as much as possible. With this potential of likening oneself to the stars, Galen builds on Plato’s association of the rational soul with the stars, and retains the Platonic ideal of ὁμοίωσις θεῷ in an altered form. Thereby, he reserves some room, at least, for the possibility of a philosophical life devoted to self-improvement.

Galen develops this position on human nature, I believe, not as his ‘philosophy’ in the sense of a dogmatic position that should, as such, be considered definitively proven, true, adhered to and defended; but, rather, as a tentative position that is best able to explain what he considers to be the empirical facts. Importantly, this tentative position should also be compatible, for Galen, with the possibility of the philosophical life just mentioned.

He roots this position in the philosophical and medical tradition by starting from a synthesis of Hippocrates and Plato. The basis for this was laid in PHP, where Galen demonstrates, basing himself on the Timaeus, how each part of the soul has a specific seat in the body and is dependent for its functioning on a specific organ and its connections to the rest of the body. He continues to build on this basis in QAM and HNH. With the important addition of Aristotelian hylomorphism, however, he is able to further integrate his interpretations of Hippocrates and Plato into a notion of a common hylmorphic nature of everything. Through this common hylomorphic nature Galen synthesizes their work in a new tentative philosophical anthropology that problematizes the duality of body and soul, which framed the original distinction between Hippocrates and Plato. Tentative, because, as we have seen, Galen also frequently casts doubt on the extent to which his physiological explanations do justice to the intelligent design he observes in nature. Finally, the fact that Galen provides a firmly physiological explanation of melancholy, in which the qualities of the black bile determine the specific symptoms and experiences of the melancholic, proves that his notion of human nature, as it appears from our analyses, finds at least some concrete application in Galen’s work.

Galen, through his own willingness to express his ignorance about subjects of speculative nature, and through his contempt for dogmatism and adherence to schools, has facilitated an understanding of his work that emphasizes the limitations of his philosophical aspirations. However, I believe that, in this book, I have shown that Galen does take position in and significantly adds to the debate on philosophical questions such as those on the substance of the soul, the relation between body and soul, and human nature. Furthermore, I think that I have shown that these positions on speculative questions are thoroughly connected to the rest of Galen’s work. He bases these views on his more concrete work concerned with the human body, on what he considers the empirical evidence with regard to a specific question, and on their usefulness with regard to ethics.