Handbook of the History of Logic: - Fordham University Faculty

Medieval Modal Theories and Modal Logic 515
through Averroes’s works in the thirteenth century. 21 Following the Averroistic
view, Thomas Aquinas and Siger Brabant, his contemporary in Paris, defined
necessary natural causes as causes which, when actual as cause, always bring
about their effect. Contingent causes are divided into those which bring about the
effect in most cases (ut in pluribus) and are in a few cases prevented by chance
and those which are not associated with a natural tendency to a definite result
(ad utrumlibet). A particular cause is here considered necessary or contingent
depending on how causes of the same type usually behave. Similarly, the effect
which is necessary with respect to its actual causes can be called contingent by
referring to what happens in other similar cases. 22 In asking how things can be
contingent if they are eternally known by divine omniscience and included in the
immutable providential plan, Aquinas sometimes states that things are contingent,
if their proximate causes are not necessary, i.e., causes which always bring about
their effect. 23
While the conceptions of power and potentiality were widely regarded as essential
elements in understanding modality, Anselm of Canterbury attempted to base
the whole of modal semantics on these notions. Putting forward a detailed analysis
of direct (proper) and indirect (improper) modes of agency, he suggested that the
lated in Stump 1988, 162-3.
21 For Averroes’s view of causation, see A. Maier Die Vorläufer Galileis im 14 Jahrhundert
(Rome: Edizioni di Storia e Letteratura, 1949), 219-50.
22 See Siger of Brabant, Quaestiones in Metaphysicam: Edition revue de la Reportation de
Munich, texte inédit de la Reportation de Vienne, ed. W. Dunphy, Philosophes médiévaux
24 (Louvain-la-Neuve: Editions de l’Institut Supérieur de Philosophie, 1981), 369.51-370.81;
378.58-380.26; De necessitate et contingentia causarum in J. Duin, La doctrine de la providence
dans les écrits de Siger de Brabant, Philosophes médiévaux 3 (Louvain: Editions de l’Institut
Supérieur de Philosophie, 1954) , 28.10-30.49; 32.1-34.34; Thomas Aquinas, Scriptum super libros
Sententiarum, ed. P. Mandonnet and M.F. Moos, 5 vols (Paris: Lethielleux, 1929-56), I.38.1.4-5;
Summa contra gentiles, ed. C. Pera, P. Marc, P. Caramello (Turin: Marietti, 1961-7), I.67.3; De
malo, ed. P.BazziandP.M.PessioninQuaestiones disputatae, vol. II (Turin: Marietti, 1965),
16.7; In Peri herm. I.13, 172; 14, 194, 197; In octos libros Physicorum Aristotelis expositio, ed.
M. Maggiòlo (Turin: Marietti, 1954), II.8.210.
23 Scriptum super libros Sententiarum I.38.1.4-5. While repeating this view in his later works
(Summa contra gentiles I.85.4; III.72.2; Summa theologiae I.14.13, ad 1), Aquinas qualified it
stating that he did not mean that things could be considered necessary as such. He stressed
that God as the first cause provided things which naturally necessary or contingent causes so
that contingent events, particularly the acts of free will, were not reducible to a necessitating
ultimate cause, though dependent on God’s irresistible will which transcended the natural orders
of necessity and contingency (Quaestiones disputatae I: De veritate, ed. R.S. Spiazzi (Turin:
Marietti, 1964), 23.5; In Peri herm. I.14, 197; see also H. Goris, Free Creatures of an Eternal
God: Thomas Aquinas on God’s Infallible Foreknowledge and Irresistible Will (Utrecht: Thomas
Instituut, Leuven: Peeters, 1996), 293-302). Siger of Brabant refers to some Parisian masters
who argued that associating the modality of an effect with that of its proximate cause was
compatible with metaphysical determinism (De necessitate et contingentia causarum 26.67-79).
In order to avoid this, he stated that the first cause left room for individual coincidences the
results of which were not known even by divine foreknowledge (De necessitate et contingentia
causarum 26.80-28.9; 31.78-32.00; 42.10-25). When accused of heresy, he became more cautious
when speaking about indeterminate events in nature (Quaest. in Met. (Vienna), 370.1-387.89; R.
Hissette, Enquête sur les 219 articles condamnés à Paris le 7 Mars 1277, Philosophes médiévaux
22 (Louvain: Publications Universitaires, Paris: Vander-Oyez, 1977), 42-3.