Human reproduction is a famous crux of Aristotelian biology. Aristotle must explain not only how higher and higher states of actualization are brought about in the fetus, but also how an immaterial intellect (if it is immaterial) comes to be produced from or associated with an animal body. Thomas grapples with these issues in numerous places, but mostly from Aristotelian sources and in contention with Aristotelian interpreters. There are only a few other sources, and they had entered Aristotelian discussion in a previous generation. For example, Thomas quotes a verse on the periods of gestation that is known from Salernitan writings, but it is also found in Michael Scot and in Albert's Sentences-commentary.34
Thomas treats human reproduction in four texts that are extensive enough to invite chronological reading. The main doctrinal lines are laid down in the Sentences-commentary, while discussing the creation of Eve. The two pertinent articles ask whether parents transmit the human soul as a whole and the
34 Scriptum Sent. 22.214.171.124. See also C. M. Joris Vansteenkiste, "'Versus' dans les œuvres de Saint Thomas," in St Thomas Aquinas 1274-1974, 1:77-85, at p. 80.
sensible soul in particular.35 Thomas holds that the rational soul is not received from the parents: being immaterial, it cannot be transmitted by material means. Thomas's argument here takes the form of a schematic doxography that contrasts the views of Plato, Avicenna, and Themistius with those of Aristotle and Averroes. The Platonic group, says Thomas, holds for a separate cause in human reproduction; its adherents are misled both by the limited properties of bodies and by a general prejudice in favor of separate causes. The Aristotelian camp holds more generous views about natural causality, making an exception only for the intellect itself. Thomas defends the Aristotelian causal view and then inserts a longish description of the processes of human generation.
The description follows Aristotle on disputed points: the origin of human seed from the last residue of unassimilated food, the presence in the seed of an indistinct potency, and the failure of the female to contribute formally to generation.36 Human seed contains "formative power" (virtus formativa), a diffuse vital energy deriving from the father. The formative power uses the vital spirit enclosed in the seed as its "instrument," its "subject," and its "organ." To this bodily spirit there is joined a threefold heat: the consuming "elementary heat" (calor elementaris), the life-giving "heat of the soul" (calor animae), and the species-bearing "celestial heat" (calor caeli). By means of these three, the fetal material is formed into the embryo's cerebral membranes. Thomas seems here to allow some material contribution from the seed to the embryo, though this contribution is denied by Aristotle.37 The activation of the potential soul in the embryo requires the assistance of the power of the celestial sphere. A series of forms is acquired and then lost until the whole rational soul is created by God.
I said that the treatment was largely Aristotelian, but it would be more precise to call it Albertist. Albert's long treatments of reproductive physiology come in the "paraphrases" of the Books on Animals and related questions. On the current chronology, these would fall in and after 1258, that is, after even the final redaction of Thomas's Scriptum on the Sentences.38 But there is already a substantial treatment in Albert's Summa of Creatures, which he completed before 1246 and which represents his teaching at or before the time
36 Scriptum Sent. 126.96.36.199.
37 Scriptum Sent. 188.8.131.52 and ad 4; compare 184.108.40.206 ad 3, which is more fully discussed below. Compare Aristotle, Degeneratione animalium 1.21 (729bl-730a32), 1.22 (730b9-31).
38 See the editorial remarks by Ephrem Filthaut in Cologne Opera omnia, 12: xlv-xlvi; compare Weisheipl, Friar Thomas, pp. 358-359.
when Thomas joined him in Paris.39 The Summa of Creatures provides the key to Thomas's treatment in the Scriptum. Three of the objections in the first article correspond exactly to the first three of Albert's arguments after Apolli-naris.40 The doctrine of the triple heat serves as the centerpiece of Albert's mechanical explanation.41 Albert also speaks of heat as the instrument of generative power.42 But the most important dependence is structural: Thomas's grouping of previous opinions corresponds to the dialectic in Albert, who contrasts the view of "Plato, Avicenna, Theodorus and others following them" with those of Aristotle.43 If the dialectic is the same, so is the line of resolution. Thomas's ambiguity about the material contribution from the male seed is borrowed from Albert, who distinguishes the material seed from the efficient and who describes the use of the seed's humidity in generating the embryo.44 The most striking change Thomas makes is to simplify the textual structure of the treatment by condensing arguments and eliminating authorities, especially medical ones. Albert alludes, for example, to the history of the quarrel between Aristotle and Galen.45 Thomas passes over the controversy in silence, preferring to concentrate on philosophical controversies concerning the embodiment of intellect.
So far I have dealt with Thomas's commentary on the Sentences. His three other texts can be reviewed much more quickly, with an eye only to significant differences. The treatment in Against the Gentiles spreads over four chapters within a polemical defense of Thomas's views on the intellect.46 Much is familiar.47 The noticeable changes are rhetorical: Thomas is moving
39 James A. Weisheipl, "The Life and Works of St Albert the Great," in Albertus Magnus and the Sciences: Commemorative Essays 1980, ed. Weisheipl (Toronto: PIMS, 1980), 13—41, at pp. 22-23 and 25.
40 Compare Scriptum Sent. 220.127.116.11 arg. 2-3 and 7 with Albert, Summa de creaturis 18.104.22.168 objs. 1-3 (Borgnet Opera omnia 35:148).
41 Albert, Summa de creaturis 22.214.171.124 ad 14 and ad 22-24 (Borgnet Opera omnia 35:157, 159-160).
42 Summa de creaturis 126.96.36.199 (Borgnet Opera omnia 35:161-162).
43 Summa de creaturis 188.8.131.52 arg. 26 (Borgnet Opera omnia 35:152).
44 Summa de creaturis 184.108.40.206 ad 2 and 220.127.116.11 ad sed contra 11-13 (Borgnet Opera omnia 35:145, 161). The deeper authority is probably Avicenna; see Thomas S. Hall, "Life, Death, and the Radical Moisture," Clio Medica 6 (1971): 3-23, at p. 4.
45 Summa de creaturis 18.104.22.168 sed contra 15 (Borgnet Opera omnia 35:155).
47 There are familiar references to bisected worms and triple heat in Contra gent. 2.86 (nos. 1,708 and 1,738; 1,710). The three counter-positions against which Thomas constructs his own view are borrowed from Albert: Contra gent. 2.89 (no. 1,736) = Summa de creaturis 22.214.171.124 sed contra 15; Contra gent. 2. 89 (nos. 1,737-1,738) = Summa de creaturis 126.96.36.199 sed contra 14. The double view on the material role of the seed persists, though Thomas approaches the more strictly Aristotelian position in Contra gent. 2.89 (nos. 1,742-1,743).
further from sources in physics and medicine. Here he emphasizes arguments against the view that the human soul can be transmitted by material means, but the argument is now also directed against more explicitly theological authorities. One of the most prominent in these chapters of Against the Gentiles is "Gregory of Nyssa," that is, both Gregory of Nyssa's On the Making of Man and Nemeslus of Emesa's Premnon physikon.48 Nemeslus already stood behind Albert's treatment, of course, but now appears explicitly (albeit pseudonymously) in Thomas.
Thomas shifts even further towards theological authorities in the questions On Power. The issue is whether rational souls are created or transmitted. Thomas invokes the collection On Ecclesiastical Dogmas twice in order to set aside opposing views as heretical.49 The most striking passage is the reply to the ninth objection. Longer even than the body of the article, it might seem (at last) to supply a technical discussion of the human seed's progressive actualizations. In fact, the reply is an amplified version of the parallel in Against the Gentiles. Its five counter-positions, for example, are variations on the three main views rejected in the earlier text.
Thomas's final treatment of human generation appears in two questions at the very end of Summa 1. The large context here is the distinction of creatures; the small context, certain special questions about the actions of bodies. Thomas is now more strictly Aristotelian about the material contribution of the male seed.50 Alternative opinions about embryonic actualization, so lengthily considered in Against the Gentiles and On Power, are passed over with a single reply.51 The authority of On Ecclesiastical Dogmas reappears prominently,52 together with a host of familiar authorities from Aristotle and Averroes. The only structural achievement is to clarify the origin of seed by interposing an article on nutrition (the doctrine of which I will consider below).
The textual transit from the Sentences-commentary to the Summa suggests some general observations. Thomas begins by simplifying the medical and physical material contained in Albert. This simplification is accompanied by a shift to philosophical authorities and issues. At no point is the issue an
48 Contra gent. 2.88 (nos. 1,728—1,733), 2.86 (no. 1,713). The textual parallels to the De opift-cio hominis cited by Marc are not compelling. For the availability of the Latin versions of that work, see the essay by Helen Brown Wicher in Catalogus Translationum et Commentariorum 5 (1984), 1-250, at pp. 120-127.
49 Depotentia 3.9 corpus and ad 9.
52 Summa theol. 1.118.2 sed contra,3 sed contra.
empirical one for Thomas, as it sometimes is in Albert.53 Thomas is concerned, rather, with the twin questions of generation by actualization and the unity of substantial forms. So his treatment is brought increasingly under the control of theological authorities. Over the transit, Thomas comes to correct himself at the one point where he had sided with the medical tradition, the material contribution of human seed. This correction must be placed in the larger context of the teaching about "root moisture."
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