[Question 4: Whether a man can arrive at any conclusion in
a demonstration by his natural capacities, without the illumination
of any superior agent.]
4.1 LET IT BE ASKED WHETHER a man can arrive at any conclusion in a demonstration by his natural capacities, without the illumination of any superior agent.
4.2 <FIRST ARGUMENT> Proof that a man can: for a natural desire is not for anything impossible, but man naturally desires to know every conclusion of a demonstration. Therefore he can arrive at cognition of them through natural principles.
4.3 <SECOND ARGUMENT> Moreover, everything contained under the primary object of its natural capacity is a per se object of that capacity, since whatever is per se in the higher is per se in the lower, even if it is not <itself> primary. For instance, this is clear with color and those that are contained under it in respect of the visual capacity. And this is clear from argument thus: a capacity restricts its primary object in such a way that it is adequate to it, but if something is contained under that object in which that capacity is not capable, then that object exceeds that capacity, and consequently is not an object adequate to it. But the first object of our intellect is being (ens) in its commonness, as it extends to every being. Therefore we can cognize naturally by our intellect whatever is contained under being, and consequently every conclusion of a demonstration.
4.3 <THIRD ARGUMENT>: Moreover, no supernatural cognition is necessary to the senses for the purpose of their cognizing any sensible, as is obvious enough. Therefore, neither <is any supernatural cognition necessary> to the intellect for it to cognize any intelligibe, for since nature is not lacking in what is necessary, it is especially not lacking in what is necessary for more perfect realities. Hence the Philosopher in On the Heavens says that it is absurd to say that nature gives a power of progression to the stars if it gives no organ to them for advancing. Since, then, nature is not lacking in what is necessary to the senses unless the senses can acquire their perfection from purely natural <causes>, much more will it not lack <what is necessary> to the intellect.
4.4 <FOURTH OBJECTION>: Moreover, whoever can cognise a principle naturally can cognize every conclusion naturally that is contained in that principle, for the cognition of the conclusion does not depend on anything except the cognition of the principle and the deduction of the conclusion from the principle, and the deduction is evident from the dici de omni or dici de nullo. But we naturally understand first principles in which all conclusions are naturally contained, therefore we can cognize all conclusions from purely natural <premisses>. Now it is clear that we cognize first principles by nature, since a first principle has the most general terms which are conceived by all, and we cognize a principle inasmuch as cognize its terms, etc. And all conclusions are contained in first principles, since because the terms of a first principle are most general that contain every particular concept and these being distributed, a distribution arises for all.
4.5 ON THE OTHER HAND, if it is thus, then a man can cognize from natural causes alone everything that the first cause knows, which is absurd.
4.6 IN RESPONSE TO THIS QUESTION, philosophers respond in one way and theologians in another. Philosophers say that man can <acquire> cognition necessary to himself from purely natural <causes>, and this is from the worth of nature, which can acquire its own perfection. This is the intention of the Philosopher in the third book of On the Soul, when he says that the agent intellect, which is active in respect of every intelligible, and the passive <intellect>, which is passive in respect of every intelligible, are naturally in the soul. Therefore from these the knowledge of every intelligible can be caused.
4.7 This is strengthened thus: To every passive natural capacity there corresponds an active natural capacity, but the possible intellect is naturally passive in respect of every intelligible, for it is naturally inclined to cognizing every intelligible, and therefore it is a passive capacity in respect of every intelligible. Therefore a natural active capacity <in respect of every intelligible> corresponds to it. <Now,> since that capacity is vain in nature which cannot be brought to actuality <that is, actual operation> through something in nature, therefore in the soul there are natural capacities through which it can <actually> acquire a cognition of every intelligible.
4.8 In another way, others<, that is, some theologians,> say that there are some things that can be cognized purely through natural <capacities> and some that cannot. Hence it is said that of all intelligibles having an order such that the later is naturally suited to be cognized through what precedes, if it is possible to cognize the first through purely natural <capacities>, then <it is> also <possible to cognize> the later <intelligibles thus>. And so, if a man can attain to a cognition of first speculative principles by purely natural <capacities>, he will be able to attain to the cognition of what follows from the principles, and if <he is> not <able to attain to> the principles, then not to the conclusions either. But in some cognizables the first of them cannot be cognized or known by natural <capacities> alone, but only by a special illumination of the first cause, for instance, in those that are believable without qualification. And in such a man cannot know anything by purely natural <capacities>. So even philosophers who have an acute natural intellect, even though they are logicians, will have doubts about the final end, or will be mistaken concerning it. Hence the Philosopher said that happiness is the acquisition of cognition, and if he understood that this was the end of this life, still he was in doubt whether there was another life. Hence everyone following natural reason concerning the end either is mistaken or has doubts about what the end is. Nonetheless, even if a man cannot arrive at cognition of such things through natural capacities, he can know and understand that that they coincide with man through purely natural <capacities>. Otherwise, a man would have no operation arising from his purely natural <capacities>, and thus he would be in this way inferior to all other creatures.
4.9 But here some say that these actions of knowing and understanding through which man acquires his perfection are in need of a special illumination because of their worth. Now although the others carry out their actions through purely natural <capacities>, this is due to the imperfection of their actions. And it is not absurd that one reality should need several things in order to proceed in its operation, while another reality needs fewer in order to proceed in a less perfect operation. But this does not seem like the truth, that among natural realities man should be the most perfect, and still that man has no perfection from his purely natural capacities, since a natural reality is called perfect because it is naturally in perfect operation.
4.10 <AS FOR THE FIRST ARGUMENT>, according to this it must be said that a natural desire is not in vain, nor does a man desire naturally to know every conclusion of demonstration, but only that in which he can know through purely natural <capacities>.
4.11 AS FOR THE SECOND, it must be granted that everything contained under the primary object of a capacity can be grasped per se by that capacity in a simple grasping. And therefore everything contained under the object of the intellect can be cognized by the intellect by a first operation of the intellect, but the intellect does not possess by nature the judgment whether it is true or not.
4.12 AS FOR THE OTHER <THE THIRD>, <it is replied> that since nature does not lack in what is necessary, therefore a man from purely natural <means> is capable in the cognition of everything which is necessary to him insofar as he is a natural being. But in this way the cognition of everything among believables is not necessary.
4.13 AS FOR THE OTHER <THE FOURTH>, <it is replied> that since he is capable naturally in the cognition of this, “everything either is or is not,” therefore he is capable naturally in the cognition of everything following on this. And therefore a man is capable naturally in the cognition of this, “God either is nor is not,” and thus for every such <proposition>. But from this it does not follow that he is capable in the cognition of this, “God is or God is not triune.,” and thus fro the others, since none such are included in this, “everything either is or is not.”