1 See Fritz Zimmermann, ‘Philoponus’ impetus theory in the Arabic tradition', in Richard Sorabji (ed.), Philoponus and the Rejection of Aristotelian Science, London: Duckworth, 1987, pp. 121–129; Franco, Abel B., ‘Avempace, projectile motion, and impetus theory’, Journal of the History of Ideas (2003), 64, pp. 521–546CrossRefGoogle Scholar, pp. 528–532; Jürgen Sarnowsky, ‘Concepts of impetus and the history of mechanics’, in Walter R. Laird and Sophie Roux (eds.), Mechanics and Natural Philosophy before the Scientific Revolution, Dordrecht: Springer, 2008, pp. 121–145, pp. 121, 129–130. On the issue of precursors to Philoponus see Michael Wolff, ‘Philoponus and the rise of preclassical dynamics’, in Sorabji, op. cit., pp. 84–120, pp. 98–105. A different version of the current paper was published as Johannes Fritsche, ‘Zur Entstehung der Impetustheorie in der Scholastik’, in Friedrich Rapp (ed.), Begriffswandel und Erkenntnisfortschritt in den Erfahrungswissenschaften, Berlin: TU-Dokumentation, 1987, pp. 149–169.

2 Aristotle, Physics VIII, 10, pp. 266b28–267a20; see also Physics IV, 8, pp. 215a14–215a17, and Aristotle, On the Heavens III, 2, p. 301b17–301b30.

3 For the purposes of my paper I can leave aside Graham's claim that the account of motion in Physics II, 1, differs from that in Physics VII, VIII, and related texts. Daniel W. Graham, ‘The metaphysics of motion: natural motion in Physics II and Physics VIII’, in William Wians (ed.), Aristotle's Philosophical Development: Problems and Prospects, London: Rowman & Littlefield, 1996, pp. 171–192.

4 Aristotle, Physics VII, 1, pp. 241b33 ff.

5 Aristotle, Physics VII, 1, pp. 242a50 ff.

6 Aristotle, Physics VII, 1, pp. 242b58 ff. There is no need for spatial contact in the case of voluntary motions caused by the soul; the Prime Mover does not move as an efficient cause.

7 Aristotle, Physics II, 1, pp. 192b16 ff.; see Aristotle, Nicomachean Ethics III, 1, p. 1110a1. Every natural movement has an internal principle of movement (Aristotle, Physics II, 1, pp. 192b21 ff.). The Scholastics debated whether this principle was an active or a passive one (see below, in my third and fifth sections).

8 Aristotle, Physics VIII, 10, pp. 266b28–267a12.

9 Aristotle, Physics VIII, 10, pp. 266b30–267a8.

10 Aristotle, Physics VIII, 10, pp. 267a8 ff.

11 E.g. Franciscus de Marchia; the pertinent text is reproduced in Anneliese Maier, ‘Die Impetustheorie’, in her Zwei Grundprobleme der scholastischen Naturphilosophie, Rome: Edizioni di Storia e Letteratura, 1951, pp. 166–180 (with a numeration of the lines), p. 168 (ll. 86–93), in part translated into English in Marshall Clagett, The Science of Mechanics in the Middle Ages, Madison: University of Wisconsin Press, 1959, pp. 526–531, p. 527; Maier, op. cit., pp. 116–122, pp. 225–226; Richard J. Hankinson, ‘Science’, in Jonathan Barnes (ed.), The Cambridge Companion to Aristotle, Cambridge: Cambridge University Press, 1985, pp. 149–150; Sarnowsky, op. cit. (1), p. 124. Wolff maintains that Aristotle aims at the idea that each layer of air behaves like an elastic body in which, through being pressed from outside, a force is activated that moves the projectile longer than the layer of air has been moved – a theory that excludes any transmission causality (Wolff, op. cit. (1), p. 90). However, Aristotle says that air can be instrumental to the force in question for a movement upward as well as downward because air is by its nature both light and heavy (Aristotle, On the Heavens III, 2, p. 301b17–301b30). This fits to the traditional assumption that the force moving upward is received by the air and not by the stone (for the latter is by nature only heavy), but rules out Wolff's suggestion as the capacity of a body to regain the shape it had before it was pressed is independent of any specific direction.

12 Both Franciscus de Marchia (Maier, op. cit. (11), pp. 177–180 (ll. 388–484)) and Buridan (Johannes Buridanus, Kommentar zur Aristotelischen Physik, Paris, 1509; repr. Frankfurt: Minerva, 1964, p. 120vb) apply the impetus theory also to the heavenly bodies.

13 Wolff, op. cit. (1), p. 84; see also pp. 85, 109.

14 Michael Wolff, Die Geschichte der Impetustheorie: Untersuchungen zum Ursprung der klassischen Mechanik, Frankfurt: Suhrkamp, 1978, p. 17 (‘Übertragungskausalität’); see Hans Blumenberg, Die kopernikanische Wende, Frankfurt: Suhrkamp, p. 27 (‘übertragene Kausalität’). All translations, unless otherwise noted, are my own.

15 Wolff, op. cit. (1), p. 91; see Maier, op. cit. (11), p. 115 (‘Berührungskausalität’); Blumenberg, op. cit. (14), p. 27 (‘begleitende Kausalität’).

16 Wolff, op. cit. (14), p. 169.

17 Thomas Aquinas, Summa theologiae, Rome: Editiones Paulinae, 1962, p. 532 (I, q. 115, a. 1, resp.); idem, Summa contra gentiles III, pars prima, Darmstadt: Wissenschaftliche Buchgesellschaft, 1990, p. 288 (c. 69).

18 Aquinas, Summa theologiae, op. cit. (17), p. 533 (I, q. 115, a. 2, resp.); idem, Summa contra gentiles III, op. cit. (17), pp. 286–298 (c. 69). For further examples see below, in this and the following sections. In Physics I, Aristotle investigates the internal principles of bodies subject to movement and argues in I, 7–9, that every body consists of matter, one essential form and various accidental forms; when change takes place, matter acquires a form that it did not have before. In Physics II, he investigates other types of cause of movements and in Physics III, 1–3, he summarizes the main results of Books I and II in terms of the notion of movement. He begins by defining movement in terms of something movable (Aristotle, Physics III, 1, pp. 201a9–201a15), but broadens the scope in order to include the relation between the movable and the external mover: ‘Movement is the actualization of the movable qua movable, and this happens through touch by that which is capable of moving so that the latter is at the same time also acted upon. Still, the mover will always carry along with it a form – a substantial one, a quality, or a quantity – which will be the principle and cause of movement when the mover moves as, for instance, an actually existing human being produces another human being out of something [the menses] that is potentially a human being’ (Aristotle, Physics III, 2, p. 202a6–12). The mover reduplicates the form that it carries along with it in the matter that it acts upon, as when an educated physician teaches students of medicine in virtue of the form of medicine. God does, on a different scale, the same thing as is implied in a comparison that Aquinas uses in the last of his five proofs of God's existence, and which is, in principle, pertinent to the issue of the impetus theory: ‘Things that do not have cognition do not strive toward an end unless they are directed by something that has cognition and intelligence as an arrow is directed by the archer’ (Aquinas, Summa theologiae, op. cit. (17), p. 14 (I, q. 2, a. 3, resp.)). Aristotle's definition of movement is – along with Plato's Phaedo (pp. 96a–107a) – the ‘origin’ of the notion of causality according to which the cause already has to have, either formally or eminently, that which it gives to the effect, the notion of causality that dominated Western ‘mainstream’ philosophy until the beginning of modernity (see Johannes Fritsche, ‘Efficient causation as donation, from Aristotle to Descartes and Gassendi’ (manuscript)). For a history of this concept of causality from a Neoplatonic perspective see Philipp W. Rosemann, Omne agens agit sibi simile: A ‘Repetition’ of Scholastic Metaphysics, Leuven: Leuven University Press, 1996.

19 Michael Wolff, ‘Mehrwert und Impetus bei Petrus Johannes Olivi: Wissenschaftlicher Paradigmenwechsel im Kontext gesellschaftlicher Veränderungen im späten Mittelalter’, in Jürgen Miethke and Karl Schreiner (eds.), Sozialer Wandel im Mittelalter: Wahrnehmungsformen, Erklärungsmuster, Regelungsmechanismen, Sigmaringen: Jan Thorbecke Verlag, 1994, pp. 413–23, p. 414, original emphasis.

20 The sentence that movement is a means, an instrument (of the first kind; see below, note 113), follows from the teleological character of many movements (Aristotle, Physics II, 8, 9, pp. 198b10–200b8) and the definitions of movement (see above, note 18) inasmuch as movement presupposes a form in the mover and terminates in the reduplication of that form in the movable, the matter acted upon. Since it is a means, the notion of causality as donation of something that the cause already has (see above, note 18) does not apply to it. Precisely because of that notion one could argue that in order to move the body the soul has to be in motion, for ‘nothing can move unless it itself is moved, since nothing can give to something else something that it does not have as, for instance, something that is not warm does not warm other things’ (Aquinas, Summa theologiae, op. cit. (17), 343 (I, q. 75, a. 1, arg. 1)). In his response to this claim, Aquinas adduces conventional Aristotelian characterizations of movement (‘to proceed from potentiality to actuality’, ‘the mover gives that which it has to the movable inasmuch as the mover brings it about that the movable is in actuality’) and points to Aristotle's proofs of the immobility of movers in Physics VIII (Aquinas, Summa theologiae, op. cit. (17), 344 (I, q. 75, a. 1, resp.)). It is through movements that movable things acquire forms; movement is none of the causes and none of the effects but rather an instrument (or an instrumental cause) of the propagation and acquisition of forms, and as such it does not need to pre-exist in the principal efficient cause.

21 See e.g. Aristotle, Metaphysics IX, 1, pp. 1046a9–29, IX, 2, pp. 1046b4–24, with the same term – ‘capacity to move’ (dunamis tou kinein) – as in the passage on the projectile and in the theory of sexual reproduction.

22 The Scholastics distinguished between different kinds of being one. Individual substances (each horse, human being and so on) and individual accidents (Socrates' knowledge of grammar, the whiteness of that wall over there and so on) differ inasmuch as the former cannot be in something else while the latter are always in something else (namely in an individual substance). However, they have in common that each of them is a single entity that cannot be multiplied or in many entities. Thus each of them is ‘numerically one’ or ‘one by number’. A species, too, is an entity that is one. However, it is in many different individuals and is not an individual. Thus it is not numerically one but ‘one according to species’. Similarly, a genus is ‘one according to genus’. The heat in the fire is numerically different from the heat that the fire produces in the stone, but the peculiarity of the force in the male semen is that it moves as numerically one and the same entity from the male into his semen and from there into the menses (see below, in this section).

23 Aquinas, Summa contra gentiles III, op. cit. (17), p. 298 (c. 69). Hence it would be ridiculous to say that a body cannot act because an accident cannot transit from one subject to a different one (Aquinas, Summa contra gentiles III, op. cit. (17), p. 298 (c. 69)).

24 Aquinas, Summa theologiae, op. cit. (17), p. 2173 (III, q. 62, a. 1, resp.).

25 Aquinas, Summa theologiae, op. cit. (17), p. 533 (I, q. 115, a. 2, ad 5).

26 Aquinas, Summa theologiae, op. cit. (17), p. 533 (I, q. 115, a. 2, ad 5).

27 See Aristotle, On Generation of Animals I, 18–20, pp. 724a14–729a33.

28 Aristotle, On Generation of Animals I, 19, pp. 726b18 ff. and elsewhere.

29 Aristotle, On Generation of Animals II, 1–8, pp. 733b23–749a6.

30 Thomas Aquinas, Summa contra gentiles II, Darmstadt: Wissenschaftliche Buchgesellschaft, 1982, p. 446–470 (c. 89). Aquinas argues here against a position from which it follows that ‘a force that is numerically one [virtus eadem numero] would be now only a vegetative soul and thereafter a sensitive soul so that, in this way, the substantial form itself would be continuously perfected’ (Aquinas, op. cit., p. 444 (c. 89)). When, in his own suggestion, he says that this formative force ‘remains the same [eadem manet] in the aforementioned spirit from the beginning of the formation until the end’, he self-evidently means ‘remains numerically one and the same entity’, and his point is that this numerically one and the same force cannot acquire different forms. Rather, these different forms belong not to the force, but to the subjects in which the force is and acts (the male semen and the menses/embryo); in addition, it is not the case that one and the same form of the menses/embryo is gradually perfected from, e.g., a vegetative soul to a sensitive soul; rather, the vegetative soul of the menses/embryo is destroyed and replaced with a soul that is vegetative and sensitive as well (Aquinas, op. cit., p. 448 (c. 89)).

31 Thomas Aquinas, Quaestio disputata de potentia, in S. Thomae Aquinatis opera omnia 3, Stuttgart and Bad Cannstatt: frommann-holzboog, 1980, p. 207c (q. 3, a. 11, ad 6). ‘The sensitive soul is in actuality in the semen, not according to its own form, but rather as in an active force; just like a house is in actuality in the mind of the artisan as in an active force’ (Aquinas, op. cit., p. 207c (q. 3, a. 11, ad 4)).

32 Aristotle, op. cit. (27) IV, 1–3, pp. 763b20–769b30.

33 See Aristotle, op. cit. (27) IV, 3, pp. 767b5–767b9.

34 Aristotle, op. cit. (27) IV, 3, pp. 766a18–766a21.

35 Aristotle, op. cit. (27) IV, 3, pp. 768b16 ff.

36 Aristotle, op. cit. (27) IV, 3, pp. 768b25 ff. See the summary of the Latin medieval debates of this issue in Bartholomaeus Mastrius de Meldula and Bonaventura Bellutus (Philosophiae ad mentem Scoti cursus integer 5 [In Arist. L. De anima, De gen. et corr. De caelo et metheoris], Venice, 1678, pp. 505–538).

37 See Anneliese Maier, ‘Das Problem der Gravitation’, in her An der Grenze von Scholastik und Naturwissenschaft, Rome: Edizioni di Storia e Letteratura, 1952, p. 143.

38 Maier, op. cit. (11), p. 136.

39 Aristotle, Physics VIII, 4, pp. 255b4, 10 ff., 19–29, 256a1.

40 Thomas Aquinas, In octo libros Physicorum Aristotelis expositio, Torino: Marietti, 1965, p. 541 (lib. 8, l. 8). The word impetus was frequently used in the theories of the soul and the will for all sorts of inclinations and impulses. Brute animals and sometimes also human beings ‘follow the impetus of passion’ (Aquinas, Summa theologiae, op. cit. (17), pp. 606 ff. (Ia IIae, q. 10, a. 3, resp.)) without reason and will. In William of Moerbeke's translation of the Physics, it occurs at a very prominent place, namely as translation of hormê (Aristotle, Physics II, 1, p. 192b18) (‘neque unum habet impetum mutationis innatum’, Aquinas, op. cit., p. 73 (lib. 2, l. 1, t.)), which at that place is equivalent to phusis (Aristotle, Physics II, 1, p. 192b21). On phusis in Physics II, 1 as a mover – and not, as Aquinas (see below, in this and my fifth section) and others maintain, a passive principle – see Johannes Fritsche, ‘Aristotle's usage of archê kinêseôs (“principle of motion”) and the two definitions of nature in Physics II, 1’, to be published in Archiv für Begriffsgeschichte (2010) 52.

41 E.g. Thomas Aquinas, In libros de caelo et mundo, in S. Thomae Aquinatis opera omnia 4, Stuttgart and Bad Cannstatt: frommann-holzboog, 1980, pp. 47c–48a (lib. 3, l. 7, n. 6–9); Aquinas, op. cit. (31), p. 207c (q. 3, a. 11, ad 5).

42 Aquinas, op. cit. (40), p. 541 (lib. 8, l. 8), see p. 74 (lib. 2, l. 1).

43 Aquinas, op. cit. (41), p. 48a (lib. 3, l. 7, nn. 8–9).

44 Aquinas, op. cit. (41), p. 47c (lib. 3, l. 7, n. 5). On the notion of a passive principle see Jan Aertsen, Nature and Creature: Aquinas' Way of Thought, Leiden: Brill, 1988, pp. 279–289; Leo Elders, The Philosophy of Nature of St. Aquinas, Frankfurt: Peter Lang, 1997, pp. 61–66; Sven Müller, Naturgemäße Ortsbewegung: Aristoteles' Physik und ihre Rezeption bis Newton, Tübingen: Mohr, 2006, pp. 121–127. Müller claims that Aquinas distinguishes between Aristotle's solution (the generator) and his own one, namely God as the immediate mover of the elements in their natural movements (Müller, op. cit., pp. 127–135).

45 Aquinas, op. cit. (41), p. 47c (lib. 3, l. 7, n. 6). I use in this paper ‘unnatural’ and ‘violent’ indiscriminately.

46 Maier, op. cit. (11), pp. 139–141; see also Maier, op. cit. (37), p. 159 n. 28.

47 Duns Scotus, Ordinatio II. A distinctione prima ad tertiam, in his Opera omnia 7, Civitas Vaticana: Typis Vaticanis, 1973, p. 360 (dist. 2, p. 2., qu. 6, n. 458).

48 Duns Scotus, op. cit. (47), pp. 354–355, n. 447, see pp. 363–374, nn. 465–485; see Müller, op. cit. (44), pp. 150–174.

49 William of Ockham, Summula philosophiae naturalis, in his Opera philosophica VI, St Bonaventure: St Bonaventure University, 1984, p. 246; see Müller, op. cit. (44), pp. 174–184.

50 William of Ockham, Quaestiones in librum tertium sententiarum (reportatio), in his Opera theologica VI, St Bonaventure: St Bonaventure University, 1982, pp. 64–67.

51 Ockham, op. cit. (50), p. 143.

52 See Maier, op. cit. (11), pp. 154–160. Ockham refutes in this context the impetus theory (Ockham, op. cit. (50), pp. 142–143). It is possible that he thought of Franciscus de Marchia (Maier, op. cit. (11), pp. 158–159). His argument is weak and was obviously ignored by later adherents of the impetus theory.

53 Duns Scotus's step meant, as Maier emphasizes, the abolishment of the sentence that every inanimate body is moved externally, by a different body as mover (Maier, op. cit. (37), pp. 156–157).

54 Maier, op. cit. (11), pp. 174, 176 (ll. 308–309, 374–375); Buridanus, op. cit. (12), pp. 33ra ff., pp. 74rb ff., pp. 113va ff.

55 See Anneliese Maier, ‘Das Wesen des Impetus’, in her Zwischen Philosophie und Mechanik, Rome: Edizioni di Storia e Letteratura, 1958, p. 357 n. 22.

56 Buridanus, op. cit. (12), p. 120vb.

57 Aquinas, op. cit. (40), pp. 621–622 (lib. 8, l. 22).

58 See below, in my fifth section.

59 See below, in my fifth section.

60 See below, in my fifth section.

61 Buridanus, op. cit. (12), p. 121ra.

62 Buridanus, op. cit. (12), p. 121ra.

63 Since, be it only because of the law of non-contradiction, a movement cannot be its own cause, its mover must be a form, within the projectile itself, that is a permanent form and not, like any movement, a successive one (Buridanus, op. cit. (12), p. 121ra; on the passage see also Maier, op. cit. (55), p. 355 n. 20). This permanent form, the impetus, is quickly destroyed by the essential form of the stone. Buridanus, op. cit. (12), p. 121ra.

64 Aquinas, op. cit. (31), p. 207a (q. 3, a. 11, arg. 5).

65 Aquinas, op. cit. (31), p. 207c (ad 5).

66 Aquinas, op. cit. (31), p. 207c (ad 5).

67 Wolff, op. cit. (14), p. 186 n. 49; see also Eduard J. Dijksterhuis, Die Mechanisierung des Weltbildes, Berlin: Springer, 1983, p. 202.

68 See Aristotle, On Generation of Animals, II, 1, pp. 730b18–730b22; see also e.g. pp. 734b31–735a4, 738b20–738b27; see above, in my second section.

69 See above, note 57.

70 See also the Appendix below. Wolff might object that the very assumption that, in Physics VIII, 10, Aristotle talks about a force that is transmitted to the medium is a projection of those who are, in one way or the other, already familiar with the impetus theory. See, however, above, note 11.

71 Thomas Aquinas, Quaestio disputata de anima, in S. Thomae opera omnia 3, Stuttgart and Bad Cannstatt: frommann-holzboog, 1980, p. 382b (art. 11, arg. 2).

72 Aquinas, op. cit. (71), p. 383b (art. 11, ad 2); despite this difference there is a similarity, ‘for as the finite force of the thrower moves, by means of locomotion, to a determined distance of a place so moves the force of the procreating agent by means of generation to a determined form’. Since the thesis against which Aquinas argues talks about the embryo, and since he probably assumes that no one will say that a force in the male semen stems from the female, he uses here semen in the sense of ‘menses’ (which was not unusual) or takes for granted that everyone adds in thought that the force in the male semen enters the menses. In other words, he assumes that the male semen acts on the menses according to the migration model. However, even if it acted on the trigger model, the migration model would still hold for the male semen in its relation to the male parent while the Aristotelian projectile is not moved from within. Note that, in the quote at the beginning of this section, Aquinas uses the word impulsus and not impetus. However, even if he had used impetus, he could have been thinking of Aristotle's theory of projectiles, since the word impetus was used in many ways (see above, note 40) and Aristotle's theory of projectiles already contains an impetus, a moving force that moves from one subject to another one.

73 For instance, Giles of Rome adopts Aquinas's theories of the semen and of the natural movements of the elements as well as Aristotle's explanation of the projectiles without even mentioning an impetus theory (Giles of Rome, Egidii Romani Commentaria in octo libros Phisicorum, Venice, 1509; repr. Frankfurt: Minerva, 1968, pp. 192va ff., pp. 221vb ff.), and he uses Aquinas's theories of the semen and of the natural movements of the elements, but not the impetus theory, to illustrate a point in theory of knowledge (Giles of Rome, De esse et essentia, de mensura angelorum et de cognitione angelorum, Venice, 1503; repr. Frankfurt: Minerva, 1968, p. 88rb).

74 I do not mean that Duns Scotus or anyone else must have known Aquinas's Quaestio disputata de anima. Rather, it is a matter of what becomes thinkable and desirable as a possibility after changes within a body of assumptions.

75 Maier, op. cit. (11), p. 183.

76 Maier, op. cit. (11), p. 195; see also Notker Schneider, Die Kosmologie des Franciscus de Marchia. Texte, Quellen und Untersuchungen zur Naturphilosophie des 14. Jahrhunderts, Leiden: Brill, 1991, p. 227, Wolff, op. cit. (14), p. 196; Sarnowsky, op. cit. (1), p. 133.

77 Maier, op. cit. (11), p. 170 (ll. 158–170). He gives two proofs for this thesis. First, lightness and heaviness are moving forces (of the natural movements of the elements) and do have opposites, namely each other. Each force that has an opposite is the mover not of opposite movements, but only of one movement (lightness of upward, and heaviness of downward movements). The moving force in question, however, moves indifferently in all different directions (Maier, op. cit. (11), p. 170 (ll. 160–165)). Second, no force that has an opposite is the mover of linear as well as circular movements. The moving force in question, however, moves movements of both kinds as is shown in the case of a potter's wheel (Maier, op. cit. (11), p. 170 (ll. 165–170)).

78 Maier, op. cit. (11), pp. 170–171 (ll. 170–172).

79 Maier, op. cit. (11), p. 171 (ll. 172–175).

80 Maier, op. cit. (11), p. 171 (ll. 175–180).

81 Maier, op. cit. (11), p. 171 (ll. 180–183).

82 Maier, op. cit. (11), p. 173 (ll. 239–243=Clagett, op. cit. (11), p. 529), pp. 175–176 (ll. 345–355, 370–373).

83 The interaction between two bodies of different temperatures was apparently the paradigmatic case in the treatises on action and reaction (see e.g. Jacobus Zabarella, De rebus naturalibus, Frankfurt 1607; repr. Frankfurt: Minerva, 1966, pp. 427–452). It seems to me unlikely that Franciscus de Marchia could find in these treatises a model that he could use for his first argument.

84 Maier, op. cit. (11), p. 178 (ll. 421–423).

85 See already Aristotle, Physics VIII, 4, pp. 255a12–255a18. One might object first and foremost that no accident can move as numerically one and the same entity from one subject to another one. However, Aquinas affirms this Scholastic axiom (see above, note 23), honours it in his trigger model of movement and at the same time assumes quite self-evidently that, according to Aristotle, and to the truth, a force moves as numerically one and the same entity from the male parent into the semen and the menses. Aquinas distinguishes clearly between forms and forces (see above, in my second section and notes 30 and 72), and can do so because forces as well as movements are instruments of movers to reproduce forms, and the laws regarding instruments need not, or even cannot, be the same as those for movers and forms (see above, notes 18 and 20). Franciscus de Marchia and Buridan use the notion of form in a very broad way so that also forces and movements can be called forms (see above, in my fourth section and note 63) (forms are not just the states in which movements terminate but, so to speak, everything that ‘makes a difference’ in a subject as a force or a movement certainly does). Still, they distinguish between forms of different kinds and between forms as properties of bodies and the instruments to produce them.

86 See above, note 63; Maier, op. cit. (11), p. 168 (ll. 81–82).

87 For Duns Scotus regarding the natural movements of the elements see Müller, op. cit. (44), pp. 157–172.

88 Duns Scotus, op. cit. (47), p. 364 (n. 466); for Aquinas see Aertsen, op. cit. (44), pp. 279–289; Elders, op. cit. (44), pp. 61–266; Müller, op. cit. (44), pp. 132–135.

89 Buridanus, op. cit. (12), p. 30raf., p. 31vaf.; Ockham, op. cit. (49), pp. 342–344; William of Ockham, Brevis summa libri Physicorum, in his Opera philosophica VI, St Bonaventure: St Bonaventure University, 1984, pp. 26–27; see, however, also his Expositio in libros Physicorum Aristotelis, in his Opera philosophica IV, St Bonaventure: St Bonaventure University, 1985, pp. 229, 235–236.

90 Buridanus, op. cit. (12), p. 121ra; see Franciscus de Marchia (Maier, op. cit. (11), pp. 175–176 (ll. 313–320)). Franciscus de Marchia compares the impetus with magnetism. The upward movement of a piece of iron is unnatural with regard to the natural inclination of iron but natural with regard to the force that the magnet has impressed in the iron (Maier, op. cit. (11), p. 176 (ll. 320–325)). On the magnet see above, note 50, and below, note 125.

91 Aristotle, Physics II, 1, pp. 192b23–192b27, 192b30–192b32.

92 Maier, op. cit. (11), p. 173 (ll. 246–249=Clagett, op. cit. (11), p. 529); Buridanus, op. cit. (12), p. 120vb.

93 Maier, op. cit. (11), p. 173 (ll. 254–256); for four other phenomena that the impetus theory, in contrast to Aristotle, saves see Maier, op. cit. (11), 173 (ll. 250–61).

94 Aristotle, Physics VIII, 10, pp. 267a12–267a15.

95 Buridanus, op. cit. (12), p. 120vb.

96 Buridanus, op. cit. (12), p. 120va.

97 Buridanus, op. cit. (12), p. 120va.

98 Buridanus, op. cit. (12), p. 120vb.

99 Wolff maintains, without giving any reason, that, in comparison to others, the impetus paradigm ‘seems to have no significant advantages or, at best, marginal ones that are outweighed by its serious disadvantages’ (Wolff, op. cit. (19), p. 414), and he speaks of the ‘speculative’ (Wolff, op. cit. (1), p. 85) character of the impetus theory, namely that ‘the moving force is taken first to proceed from a moving cause, then to be impressed on a moved body and, finally, to be exhausted at the end of the motion’ (Wolff, op. cit. (1), p. 85).

100 According to Maier (op. cit. (11), p. 304), the vast majority of Scholastic philosophers accepted the impetus theory around the year 1600; see also Sarnowsky, op. cit. (1), pp. 136–137.

101 Maier, op. cit. (11), pp. 126, 200; idem, ‘Impetustheorie und Trägheitsprinzip’, in her Die Vorläufer Galileis im 14. Jahrhundert, Rome: Edizioni di Storia e Letteratura, 1949, pp. 151, 154; see also Jürgen Sarnowsky, Die Aristotelisch-scholastische Theorie der Bewegung: Studien zum Kommentar Albert von Sachsens zur Physik des Aristoteles, Münster: Aschendorff, 1989, pp. 386, 402; Sarnowsky, op. cit. (1), pp. 122, 126, 136, 143–145.

102 Blumenberg, op. cit. (14), p. 27; see also idem, Die Genesis der kopernikanischen Welt, Frankfurt: Suhrkamp, 1975, pp. 171–199.

103 Wolff, op. cit. (14), pp. 58 ff.

104 Wolff, op. cit. (14), pp. 163 ff.

105 Amos Funkenstein, Theology and the Scientific Imagination from the Middle Ages to the Seventeenth Century, Princeton: Princeton University Press, 1986, pp. 167–168.

106 Christoph Flüeler, Rezeption und Interpretation der Aristotelischen Politica im späten Mittelalter, part I and II, Amsterdam and Philadelphia: B.R. Grüner, 1992, pp. 36–38.

107 Klaus-Jürgen Grün, Vom unbewegten Beweger zur bewegenden Kraft: Der pantheistische Charakter der Impetustheorie im Mittelalter, Paderborn: mentis, 1999.

108 Aristotle, Physics II, 3, p. 195a22.

109 Aristotle, Metaphysics IX, 1, pp. 1046a27 ff.

110 Aristotle, Physics III, 3, pp. 202a31 ff.

111 Aristotle, Politics I, 4, pp. 1253b23 ff.

112 Aristotle, Politics I, 4, pp. 1253b32 ff.

113 Francisco Suárez, Disputationes metaphysicae, Opera omnia 25, Paris, 1866; repr. Hildesheim: Olms, 1962, p. 592 (Disp. XVII, Sec. 2, 22).

114 Everyone will acknowledge instruments of the first kind (see above, note 64).

115 Funkenstein, op. cit. (105), p. 168.

116 Aquinas, Summa theologiae, op. cit. (17), p. 2175 (III, q. 62, a. 4, resp.). Aquinas continues, ‘in the way in which also movement is an imperfect actuality by an agent into a patient’. This sentence seems to suggest that the sacrament acts on the receiver of the sacrament according to the trigger model of movement; see also Aquinas, Summa theologiae, op. cit. (17), p. 2175 (III, q. 62, a. 4, ad 3).

117 Aquinas, Summa theologiae, op. cit. (17), p. 2173 (III, q. 62, a. 1, resp., ad 2).

118 Aquinas, Summa theologiae, op. cit. (17), pp. 2173, 2176, 2290 (III, q. 62, a. 1, resp., ad 2; a. 5, resp.; q. 78, a. 4, ad 1). At one point he refers to the human voice. Against his thesis that there is in the sacrament an instrumental force that causes grace in the recipient one could object that the force would have to be a spiritual one, which as such, however, cannot be in a body (Aquinas, Summa theologiae, op. cit. (17), p. 2175 (q. 62, a. 5, arg. 1)). Aquinas responds that a spiritual force can be in a body, not as a permanent and complete force, but as an instrumental one, and a body can be moved by a spiritual substance to induce a spiritual effect in something else, just as in the human voice there is a spiritual force that incites the intellect of the listener, and which proceeds from a mental concept of the speaker (Aquinas, Summa theologiae, op. cit. (17), p. 2175 (q. 62, a. 5, ad 1)). Probably, Aquinas regards the human voice as an instrument of the third kind. However, even if he saw in it an example of an instrument of the fourth kind, it would not matter since his argument at that point is not about the type of instrument but about the possibility of a spiritual force in a body. In addition, his analogy would lead from the human voice to the sacrament and not the other way around.

119 Jesus Christ's humanity is God's hand and the sacrament God's stick: ‘I respond by saying that, as was said, in order to produce grace a sacrament acts in the way of an instrument. There are, however, two kinds of instruments, namely separate ones as, for instance, a stick, and conjoined ones as, for instance, a hand. A separate instrument is moved by a conjoined one as, for instance, a stick by a hand. The principal efficient cause of grace, however, is God himself to whom the humanity of Jesus Christ is related as a conjoined instrument and a sacrament as a separate instrument. Hence it is appropriate that the force that brings salvation proceeds from the divinity of Jesus Christ through his humanity into the sacraments’ (Aquinas, Summa theologiae, op. cit. (17), p. 2176 (III, q. 62, a. 5, resp.)). If Aquinas had regarded a sacrament as an instrument of the fourth kind, he would have certainly adduced the semen as example.

120 Maier, op. cit. (11), p. 166 (ll. 11–19).

121 Maier, op. cit. (11), pp. 166–167, 179 (ll. 22–23, 30, 40, 458–461).

122 Maier, op. cit. (11), p. 180 (ll. 494–497); see Maier, op. cit. (11), p. 166 (ll. 11–19).

123 Maier, op. cit. (11), pp. 161–162.

124 Maier, op. cit. (11), pp. 167, 176–177 (ll. 37–47, 379–387).

125 While Aquinas construes the force in the semen (as an instrument of the fourth kind) according to the migration model of movement, he seems to construe the force in the sacrament (as an instrument of the first kind) according to the trigger model (see above, note 116). It is not impossible that Franciscus de Marchia construes the impetus (as an instrument of the fourth kind) according to the trigger model (see the Appendix below). In the Latin West, the language of ‘forces’ has proliferated since the twelfth century (see August Nitschke, Naturerkenntnis und politisches Handeln im Mittelalter. Körper – Bewegung – Raum, Stuttgart: Klett, 1967, pp. 79–113). Still, at the end of the thirteenth century only the male semen seemed to count as an instrument of the fourth kind. As also Ockham acknowledges (see above, note 50), the magnet is an instrument of the third kind since, in contrast to the male parent and the thrower, it moves only as long as it exists.

126 The Franciscan Franciscus de Marchia could certainly not get any inspiration from the Franciscan Duns Scotus, for Duns Scotus claims that no instrument contains an instrumental force, neither a sacrament nor the human voice nor any other instrument of an artisan (Opus oxon. 4, d. 1, q. 5; Reportationes 4, d. 1, q. 4). Blumenberg assumes that the impetus theory of projectiles and of the heavenly bodies and the theory of the sacraments (all as instruments of the fourth kind) worked in tandem, so to speak, with a leading role of the theory of the sacraments (Blumenberg, op. cit. (102), pp. 173 ff.). However, for the reasons mentioned this seems to be improbable.

127 Aristotle, Physics VIII, 4, pp. 255b29–256a3; for pp. 255b29–255b31 see Fritsche, op. cit. (40).

128 Aristotle, Physics VIII, 4, pp. 255b27–255b29.

129 Aristotle, Physics VIII, 4, pp. 255a30–255b5.

130 See above, note 53.

131 Maier, op. cit. (11), p. 172 (ll. 223–230=Clagett, op. cit. (11), 529).

132 Buridanus, op. cit. (12), p. 120vb.

133 Maier, op. cit. (11), p. 180 (ll. 477–478).

134 Maier, op. cit. (11), p. 180 (ll. 478–484).

135 See above, note 12.