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.⁹⁹ 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.¹⁰⁰ 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.¹⁰¹ 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.

Certitude could arise from some observable fact or experiment. There is no experiment to prove evolution.¹⁰² However, some restricted observation of evolution is possible within species and as a biological ascent.¹⁰³ Further, in art, finality is evident as the goal of the artist.¹⁰⁴ Proof of the principle of finality, noted by Aristotle, is observed from the regularity in nature, is observed from art imitating nature, and from adaptation of plants and animals that can be observed in nature.¹⁰⁵ Concerning a metaphysical proof, Gardeil cites Aquinas that movement must have a goal.¹⁰⁶ Concerning irrational creatures, St. Thomas notes: "The entire irrational world is related to God as an instrument is to a principle agent (Aquinas Summa Theologiae 1-2. 1. 2).¹⁰⁷

Certitude could arise from some philosophical explanation that exists for the need of concept of finality in Evolutionism. Explanations were given by several Neo-Scholastics, notably Klubertanz, who gave a detailed explanation of how finality works in evolution.¹⁰⁸ His view on finality was supported by Calcagno, De Finance, Dougherty, Donat, Gardeil, Glenn, Hugon, La Vecchia, and Renard. Klubertanz’s view of chance in Evolutionism was supported by Ayala, De Finance, and Nogar. Klubertanz’s view of Providence in Evolutionism was supported by Benignus and Haffner. That chance and Providence work together in Divine Concursus was supported by Benignus and Hellin.

Certitude could arise if the argumentation was based on some philosophical principles. Two arguments for finality in Evolutionism were given, one based on the principle of finality and the other based on the principle of sufficient reason.

Certitude could arise if the explanation is sufficient, due to the principle of sufficient reason. But the explanation is sufficient.¹⁰⁹

Certitude could arise if the explanation was rooted in St. Thomas Aquinas, thereby being faithful to tradition. St. Thomas has a theory of biological ascent (Aquinas Summa Contra Gentiles 3. 22) that approaches programmed evolution.

Certitude could arise if Neo-Scholastics agree on the possibility of the principle of finality as universally applicable, including applicability to Evolutionism. The Neo-Scholastics and their philosophical predecessors do agree.¹¹⁰

Certitude could arise due to recent scientific confirmation by convergent scientific arguments. Science has found that during the process of mitosis (for single-celled living things) and the process of meiosis (in bisexual reproduction), living things are particularly susceptible to outside interference, which is equivocal causality.¹¹¹ Confirmation of equivocal causality is from Stephen Scherer of the Hospital for Sick Children in Toronto who has identified 1,576 apparent random mutations between the genome of the chimpanzee and the human; more than half occurred sometime during human evolution.¹¹²

Certitude could arise if the opposite opinion is not tenable. The opposite opinion would be a denial of the principle of finality, which is not possible since the principle of finality is an analytic principle, universal and necessary.¹¹³

Certitude could arise if the objections of adversaries are able to be answered.

OBJECTION: To act toward a goal demands knowing the goal. But natural agents cannot know the goal. Therefore, natural agents cannot act for a goal. REPLY: Rational agents can act for a goal, formally and self-directing. Irrational agents can act for a goal, materially and executively, as something directed by another toward a goal, just as the arrow was shot at the target by the bowman.¹¹⁴

OBJECTION: The goal of an action, finality, is only attained at the end of the act. REPLY: The goal is first in order of intention, and last in order of execution.¹¹⁵

OBJECTION: Some Neo-Scholastics have said evolution is impossible, because of the principle of causality: the effect cannot be more perfect than the cause. REPLY: This can be answered by the theory of equivalent causality. There are multiple causes.

OBJECTION: Some Neo-Scholastics have said evolution is impossible, because of the principle of causality: the effect must be the same kind as it non-cognoscitive cause. REPLY: This can be answered by the theory of equivalent causality. There are different causes.

OBJECTION: Observable nature presents no signs of purpose or finality. REPLY: This conclusion is far from self-evident. Even the survival of the fittest in the struggle for existence has life itself as the end and goal of the struggle.¹¹⁶

OBJECTION: The chief criticism leveled at the evolutionists is based on their tendency to forget that not all evolution means progress.¹¹⁷ REPLY: The theory of equivocal causality of Klubertanz is adequate enough to explain regressive evolution.¹¹⁸ "Regressive evolution" is that type of evolution in which the offspring would be essentially less perfect than the parent, and on the scientific level an example are parasites.

Certitude can be had from the possibility of philosophers and theologians admitting this mode of origin without damage to their other beliefs.¹¹⁹

The level of certitude for "Evolutionism needs some concept of purpose," is at minimum at the level of the metaphysically certain. The proof is the principle of finality, which is an analytic principle, universal and necessary.¹²⁰ 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 Hellin, who rates this thesis "most certain."¹²¹

Having come to the correct conclusion on the philosophical level of certitude, the philosopher must still conclude with some humility. The philosophy of nature still presents some problems, even for the philosopher. First, nature is unquestionably endowed with finality. But that is not to say that one can always identify the specific end of each thing and each activity in nature.¹²² Second, when the principle "every agent acts for an end" (omne agens agit propter finem) is rigorously applied, it is to the nature, and not to the individual as such. We do not want to assign to each event a distinct finality when we say "natura nihil facit frustra" (Aquinas De Anima 3. 1. 17). The opaqueness proper to material explains the imperfect intelligibility of facts.¹²³ Third, nature is a complex reality, and the whole explanation of its course and events must be sought in all the causes. To produce a certain kind of thing, it will be necessary to use a certain kind of material; or, this kind of agent must be had to perform this kind of work. The attainment of the final goal, then, does depend, in some manner and measure, on the matter and the other pre-existing causes. The end is the principle cause and condition to which all other causes are subordinate and secondary. Whatever the material, formal and efficient causality contribute to a thing they do so by virtue of the final cause; and inversely, whatever a thing owes to them, it owes still more to the final cause. St. Thomas says, "The philosopher of nature should give both causes, namely the material and the final, but more the final, because the end is the cause of the matter but the opposite is not true. It is not true that the end is such because the matter is such, but rather the matter is such because the end is such" (Aquinas In Phys. 2. 15. 533).¹²⁴