CHAPTER LXXII—That Divine Providence is not inconsistent with an element of Contingency in Creation⁶⁵³⁶⁵³    Cf. I, Chapp. LXVII (with notes), LXXXV.
   The contingent, συμβεβηκός, is that which is, but might not be (Aristotle, Physics, VIII, v). The term is still of interest to the logician, and to the psychologist, who concerns himself with the freedom of the will, but has lost all interest in physical science, except in the cognate sense of accidental.

AS divine providence does not exclude all evil from creation, neither does it exclude contingency, or impose necessity upon all things. The operation of providence does not exclude secondary causes, but is fulfilled by them, inasmuch as they act in the power of God. Now effects are called ‘necessary’ or ‘contingent’ according to their proximate causes, not according to their remote causes. Since then among proximate causes there are many that may fail, not all effects subject to providence will be necessary, but many will be contingent.

6. On the part of divine providence no hindrance will be put to the failure of the power of created things, or to an obstacle arising through the resistance of something coming in the way. But from such failure and such resistance the contingency occurs of a natural cause not always acting in the same way, but sometimes failing to do what it is naturally competent to do; and so natural effects do not come about of necessity.⁶⁵⁴⁶⁵⁴   But a ‘natural cause,’ or physical agent, as such (res naturalis), as distinguished from a moral agent, does always act in the same way under the same circumstances. It is the circumstances that vary, not the behaviour of the natural cause. Compare Newton’s second law of motion. And so natural, or physical, events come about under an hypothetical necessity. They always happen in the same way, if the antecedents, positive and negative, are the same.
   In this chapter St Thomas is concerned to obviate a difficulty unlikely to occur to modern minds, — how it is consistent with divine providence for terrestrial events, such as the weather, the growth of the crops, the healthy development of animals, not to run in regular calculable cycles, like the ordinary celestial phenomena, sunrise and sunset, equinox and solstice, the waxing and waning of the moon. From Plato and Aristotle to Newton, celestial phenomena were ‘necessary,’ terrestrial ‘contingent.’ The real difference is one of simplicity and plurality of causes. Professor Stewart, Notes on Nicomachean Ethics, vol. II, p. 9, writes: “There is no contingency in things, but there is often failure on the part of organic beings to cope with the complexity of the necessary laws which thing obey”: a remark which is true, so far as things do obey necessary laws. But there is a contingency in acts of free will, and in things so far as they are consequent upon such acts. To take another point of view. Contingency, like chance, has been predicated of co-existences, or coincidences, rather than of sequences; and necessity has been made out for sequence better than for co-existence. The study of co-existences carries us far back into the dim past, even to that ‘primitive collocation of materials,’ which, it is argued, must have been the work of intelligence and free will. Cf. B. I, Chap. XIII: B. III, Chap. XCIV, with notes.