Yves R. Simon, Introduction to Metaphysics of Knowledge, trans. Vukan Kuic and Richard Thompson (New York: Fordham University Press, 1990): 82-83n46:
Following Aristotle, the scholastics Regularly defined life as the power of self-movement or, better still, of conferring upon oneself one's own perfection. For as Aquinas warns us, having in mind the life of the spirit, the expression "self-movement" needs here to be taken in the broadest sense in which it designates any kind of activity at all (ST I q.18 a.1). We note that many contemporary biologists, including those totally unacquainted with Aristotle, seem to accept the notion of life in full agreement with his definition. L. Vialleton, "Types d'organization et types formels," Archives de philosophie 6, no.1 (1928), 92; Hans André (a good Aristotelian), "La typologie des plantes," Cahiers de philosophie de la nature 2 (1928), 40; H. Ebbinghaus, Précis de psychologie (Paris: Alcan, 1912), 64; C.B. Grassi, La Vita: Ciò che sembra a un biologio, 4: "Anyone who thinks about the way in which a chick is hatched from an egg feels a deep astonishment. While the biologist is familiar with even the slightest details of this evolutionary process, his knowledge cannot quite dispel the feeling of aw, since what he is observing is a miracle not unlike that of a great palace rising spontaneously out of a heap of mortar and bricks without the help of any workmen, with doors and windows opening bit by bit, and window panes, shutters, balconies and furniture all coming into being and fitting in place." Ore as Plat (a mechanist, quoted by Rémy Collin, "Réflexions sur le psychisme," Cahiers de philosophie de la nature 3 , 33), puts it: "'A living being resembles a machine in motion, which, however, has the special quality of being able to maintain itself in motion; it is like a clock that rewinds itself.'"
It should be pointed out that, contrary to an opinion widely accepted these days (cf. Joseph Kleutgen, SJ, Die Philosophie der Vorzeit verteidigt [Innsbruck: Rausch, 1878], 1, 3, and Hans André, loc. cit.), neither Aristotle nor the Scholastics ever, to the best of our knowledge, identified the self-movement characteristic of life with immanent activity, and as a result they never defined life as immanent activity. John of St. Thomas provides all the needed clarifications on this subject. Within the category of action, vegetative activity, like the action of the intellectus agens (Phil. nat. III q.10, a 1 [Reiser III 303B27]), is a transitive activity, because it is essentially a production of a term; thus this activity does not really differ from the activity of inanimate things, and we call it vital only because the term it produces remains within the agent and constitutes its perfection. To call it for that reason also an immanent action betrays a totally materialist outlook. Phil. nat III, q. 1 a.4 (Reiser III 40A28ff). Now, the objection is also made that vegetative life could not really be life since all the vegetative operations are transitive actions: alteration, increase, attraction, repulsion, all of which are found in inanimate bodies (nowadays the objection would be that the scientific study of the so-called vital activities reveals nothing more than physico-chemical forces). John of St. Thomas replies: "Even though vegetative life is transitive rather than an immanent activity, it still deserves to be called life because it in fact operates of itself; this is shown in particular in the vital action of generating life, even though this, too, is a transient action and one that depends upon alteration... And so even the mode in which they are performed pertains to the species of these operations." Ibid., q.6 a.4 (Reiser III, 195B41): "Immanent action is not formally physical action, in the category of action, but a metaphysical action, in the category of quality. Immanent activity may be virtually transitive and productive [e.g., knowledge produces concepts], but as immanent, it is formally a quality. Otherwise, it would be immanent not per se and of its own nature but by reason of a term inhering in the agent itself, which means immanent not by virtue of action inasmuch as it is action but owing to a term not as achieved by action but as passively received. Such immanence or inherence of a term, whether in the agent itself or in another subject, is wholly accidental with respect to action in its character as action, because such action itself does not perfect the agent immanently nor actuate the agent. It is the coming to be of the term, and it is the term that actuates and inheres in the agent not as agent but as a subject of inherence. What does it matter for the essential distinction of an action whether its term which inheres in a subject has for subject the agent itself or some subject outside."