The purpose of this section of the dissertation is to assess the minimum level of certitude for the thesis proposed, with an additional comment of any suspected higher level of certitude. There are various levels of certitude that can be chosen. Opinion is defined as intellectual assent (or disagreement) given to one part of a contradiction with fear of the opposite.⁸² Possibility is defined as the capacity for existence for a concrete possible thing: internally, that its constituent characteristics are not impossible, and additionally externally possible, if there is power to produce the thing.⁸³ Probability, also called likelihood, is defined as the weight of motives, or the accumulation of serious motives, for prudent assent to some proposition, which is intrinsic probability if the motive arises from the nature of the thing, and can be extrinsic probability if the motive is from authority, which can also suppose the internal motive.⁸⁴ Summary of Probabilities is defined as an accumulation of probable arguments, considered according to their force, which results from a mere juxtaposition. Convergence of Probabilities is defined as an accumulation of probabilities which converge to produce a sufficient reason. Moral certitude is defined as firm assent to one part of a contradiction whose necessity arises from the moral law in the physical (not ethical) sense, e.g., every mother instinctively loves. Physical certitude is defined as firm assent to one part of a contradiction whose necessity arises from the very physical nature of the thing, e.g., the law of gravity. Metaphysical certitude is defined as firm assent to one part of a contradiction whose necessity arises from metaphysical necessity, e.g., my own existence.⁸⁵

Certitude could arise from some observable fact or experiment. However, there is no experiment to prove evolution.⁸⁶ However, some restricted observation of evolution is possible within species.⁸⁷ Nogar notes, "The theory of evolution, taken in its strict sense, cannot explain the origin of man as a whole, since it does not account fully for his spiritual and intellectual capacities, his history, nor his destiny."⁸⁸ Benignus agrees, and argues from the limitations of material.⁸⁹

Certitude could arise from some philosophical explanation that exists. Explanations were given by several Neo-Scholastics: Reynard,⁹⁰ Benignus,⁹¹ and Hugon.⁹²

Certitude could arise if the argumentation was based on some philosophical principles.

Renard bases his argument on the principle of contradiction, the primary principle of all.⁹³ Further, the argument of Renard is a priori.

Certitude could arise if the explanation is sufficient, due to the principle of sufficient reason. Both Renard, arguing from the nature of man, and Benignus, arguing from the limits of matter, have given sufficient reasons.

Certitude could arise if the explanation was rooted in St. Thomas Aquinas, thereby being faithful to tradition. St. Thomas holds that man is the apex of creation and the goal of the world. This would imply that biological evolution in man has attained its goal. St. Thomas teaches that man is the goal of creation: "It was necessary for the perfection of the universe that some intellectual natures exist" (Aquinas Summa Contra Gentiles 2. 46).⁹⁴ Both Mondin and Benignus note the teaching of St. Thomas: "...and finally the life of man. After this no later and more noble form is to be found in things that are generated and corrupted. Therefore (the appetite whereby matter seeks a form must tend to the last and most perfect act to which matter can attain as to the ultimate end of generation), the last end of all generation is the human soul and to this does matter tend as its ultimate form. Man therefore is the goal of all generation" (Aquinas Summa Contra Gentiles 3. 22).⁹⁵

Certitude could arise if Neo-Scholastics agree that man is the culmination of evolution and that present and future evolution will be cultural. Nogar holds that cultural factors will dominate biological factors in the future of man.⁹⁶ Hellin views man as the most special beneficiary of Divine Providence.⁹⁷

Certitude could arise due to recent scientific confirmation by convergent scientific arguments showing the limits of biological evolution. Villagrasa notes that recent attempts at numerical simulation only confirms micro-evolution of species, so that evolution seems possible only internal to the species.⁹⁸

Certitude could arise if the opposite opinion, that man could substantially change so as to not be a human animal or have a human soul is not tenable, according to Renard.⁹⁹ Klubertanz notes that "Psychological determinism rests on an equivocation in the term ‘the greater good’."¹⁰⁰

Certitude could arise if the objections of adversaries are able to be answered. Renard argues from the principle of contradiction: Renard views man as the terminal goal of evolution and so not open to substantial change.¹⁰¹ Renard argues that man is a rational (soul) animal (body). The true definition of man postulates this composite nature of soul and body. No efficient cause, not even God, could produce a creature possessing the nature of man which would not be composed of body and soul. Thus a man who is not rational, or a man who is not an animal, would not be a man. Man would be a non-man, which is opposed to the principle of contradiction. Any other change in man, even if due to biological evolution, would be an accidental (per accidens) change, and not result in a substantial (per se) change for new species of "man."

Certitude can be had from the possibility of philosophers and theologians admitting this mode of origin without damage to their other beliefs. Nogar notes that the theory of evolution taken in the strict sense does not fully account for man’s spiritual and intellectual capacities, his history, nor his destiny.¹⁰² Evolutionists assign the object of happiness for man to be the civil progress of the human race.¹⁰³

Certitude can be had from the fact little or no future biological evolution of man is the best answer now.¹⁰⁴ St. Thomas makes a distinction between a "verified" universal (dici de omni) and a "provisional" universal (ut nunc).¹⁰⁵ This provisional universal, within a working hypothesis, is very useful in the investigation of nature. An example of a verified universal (dici de omni) is that in a right triangle every right angle has ninety degrees. An example of a provisional universal (ut nunc) is "white" predicated as a common property of swans, or evolution predicated as the common property of every origin of species. The example of the right triangle is a property based on certain (propter quid) demonstration. The example of the white swans is based on an incomplete (quo) induction, since the reporters had never seen a black swan. Thus, the continued biological evolution of man is not likely, even though no one knows the future, because the proofs given are a priori from the nature of man as rational animal (Renard) and the limitations of matter (Benignus).

The level of certitude for "future biological evolution of man is unlikely, and equivocal" is at minimum at the level of the metaphysically certain. The proof is the principle of contradiction, says Renard.¹⁰⁶ Further, the convergence of all of the above arguments are proof, especially the fulfillment of the principle of sufficient reason. This agrees with the opinion of Renard.¹⁰⁷ Nogar agrees that the use of evolution about the future of man is a radical change in the concept of evolution, and so equivocal.¹⁰⁸ Gonzalez holds as certain that God is a necessary object of happiness.¹⁰⁹

Having come to the correct conclusion on the philosophical level of certitude about the unlikely continuation of biological evolution in man, the philosopher must still conclude with some humility. The philosophy of nature does not disregard the objects observed and perceived by sense.¹¹⁰ This is the method of Aristotle and St. Thomas.¹¹¹ Even though the resurrection of the body is not something naturally necessary for the soul to be perfectly satisfied, the resurrection of the body is naturally perceived by natural understanding and by persuasive rational arguments.¹¹² Thus the body continues to play a role in the future of man. Small evolutionary changes that might occur in the human body in the future are not easy to determine, for although the ordination of the whole universe to man is found in the order of essences, divine action respects the activity of nature to the extent that it supresses neither contingence, nor liberty, nor chance.¹¹³