See Part 1.
Early in his Institutes of Elenctic Theology, Francis Turretin states, below the question “Whether natural theology may be granted,” that “We find in man a natural law written upon each one’s conscience excusing and accusing them in good and bad actions, which therefore necessarily implies the knowledge of God, the legislator, by whose authority it binds men to obedience and proposes rewards or punishments” (1.3.5). The original question refers not to Adam’s relationship to natural law before the fall, but to it as “remained after the fall” (1.3.1). Each person, even after the fall, has knowledge both of the natural law and the Lawgiver, and from this knowledge one also knows that this divine lawgiver has authority to bind men to obedience and to reward and punish. This is all natural knowledge that has been “written” on man’s heart. Each person knows what is good and bad and knows that God exists and deserves worship. Turretin uses the universality of this knowledge of right and wrong to prove that natural theology is possible after the fall. He writes, “Universal experience confirms it. For what is commonly and immutably in all men without exception must be in them naturally because natural things agree in all and are immutable. But the knowledge of the deity is immutably in all because there is no nation so barbarous upon whom this persuasion of deity does not rest” (1.3.7). He goes on approvingly to cite Cicero’s De Natura Deorum.
As we saw with Calvin, the presence of religious observance of various kinds around the world proves that knowledge of natural theology remains. Turretin writes, “The institution of religion in the world most clearly proved natural theology” (1.3.8). This explains why Plato would call man a “religious animal.” Even the most savage of nations are not “destitute of all knowledge of [God]” (1.3.9). The knowledge of God is properly “drawn from the right of nature itself…[as evident from] the testimonies of the most illustrious heathen philosopher” such as Plato, Aristotle, the Stoics, and Cicero (11.1.17). He credits Cicero with having “various weighty arguments” for the view that justice is not based on opinion, but established by nature. Turretin goes on to cite Socrates and Plato.
While Turretin affirms that fallen and unregenerate philosophers gathered true knowledge from nature, he still thinks, with Calvin, that the fall devastated man’s ability to have sound reason. It did not, however, obliterate this ability. For all to be without excuse for their sin, there had to be knowledge of good and evil. Hence, the ability to reason had to remain adequate to this end. So he says, “Although the human understanding is very dark, yet there still remains in it some rays of natural light and certain first principles, the truth of which is unquestionable” (1.9.5). Later he writes, “For God is the author of [philosophy]…by a natural enlightenment (phanerosin) in the corrupt state of man so far as concerns truth known still by nature” (1.13.10). Reason and philosophy continue to be a means by which man can have knowledge of God and his law.
Turretin follows Calvin (and many others) in saying that the moral law in scripture is the same in substance as the natural law and that the natural law is the foundation of the moral law. He writes, “Thus the origin and foundation of this law….must be drawn from the right of nature, founding both on the nature of God, the Creator (who by his holiness must prescribe to his creatures the duties founded upon that right), and on the condition of rational creatures themselves” (11.1.8, 9). The basis or foundation of the law in scripture is the law of nature; the moral law presupposes the natural law. The moral law is simply a different mode of delivery. Turretin proves this with the following arguments. The first is that scripture, in Romans 2:14, 15, asserts that the Gentiles do the law, despite not having the written law (11.1.11). The second is the “consent of the nations” (11.1.13). Though the heathen are “without a teacher” they have “many laws concerning equity and virtue.” The third is from the “heathen philosophers,” who “bravely opposed…[the]impious opinion” that “nothing is just by nature” (11.1.16, 17). “Even Cicero,” he writes, “sufficiently proves this in his books on the law.” It is evident, on Turretin’s account, that the natural law is the foundation and the same in substance as the moral law of scripture, because the heathen nations and philosophers were able to recognize and establish just laws without the written law.
As for revelation, Turretin says that it “supposes the general knowledge of nature” (1.3.10). The additional, special revelation was not meant to abrogate anything in nature. It does not supersede it. The relationship is harmonious and complementary. The revelation of God the Redeemer is a surer testimony of natural knowledge and (principally) reveals the plan and means of redemption. He writes, “it is not repugnant that one and same thing in a different relation should both be known by the light of nature and believed by the light of faith; as what is gathered from the one only obscurely, may be held more certainly from the other. Thus we know that God is, both from nature and from faith.” Notice that when Turretin says that “what is gathered from” nature can be “held more certainly from” scripture, he is not saying that gathering truth from nature is futile, but that it is clarified by scripture. The fact that knowledge of God is revealed in scripture does not preclude seeking to gather knowledge from nature.
The accessibility of this natural knowledge of God might cause one to wonder why—if non-Christians have knowledge of God, conduct worship, and even sometimes have good conduct—are they condemned? After all, they have some knowledge that God is merciful and is a redeemer of those devoted to him (1.4.11). They can know, apart from revelation, that “he is just, wise, good; that the soul is immortal, etc.” (1.8.1). Turretin admits that in “natural theology by the light of nature some such [principles of religion] exist upon which supernatural theology is built (for example, that there is a God, that he must be worshipped, etc.)” (1.4.3). He even says that natural theology is “useful to men,” including “as a subjective condition in man for the admission of the light of grace because God does not appeal to brutes and stocks, but to rational creatures,” “an incitement to the search for this more illustrious revelation” and, sounding rather republican, “as a bond of external discipline among men to prevent the world form becoming utterly corrupt’ (1.3.4). But Turretin will not go the way of the Arminians who believed that natural knowledge of God, by itself, was sufficient to make salvation possible for non-Christians. This is why Calvin’s distinction in the duplex cognition Dei is so crucial for Reformed theology. Turretin writes:
It is one thing to allow some knowledge of God as Creator and preserver however imperfect, corrupt and obscure; another to have full, entire and clear knowledge of God as Redeemer and of the lawful worship due to him. Natural theology has the former in that which may be known of God. Revelation alone has the latter in the faith which is gained only from the word.
The means of salvation are revealed in revelation alone. The created order contains no means of salvation or redemption. There is no salvation apart from the additional revelation of grace. As he says, “There can be no saving religion without Christ and faith in him [and] Christ is revealed nowhere except in the gospel” (1.4.5). Reason has certain boundaries and within those boundaries there is no message of redemption, only condemnation. For “who will say that this could be derived from the book of nature where God manifests himself only as the Creator and preserver” (1.4.11). Knowledge of redemption comes only from an addition to the created order. But notice that Turretin does allow “some knowledge of God as Creator and preserver.” Non-Christians can have real knowledge of God and his laws.
Turretin even acknowledges that the heathen can have right conduct in temporal and external matters. They can “properly regulate their external actions.” He writes (1.4.17),
Although some of the heathen (comparatively considered and in relation to each other) may have been better than others; although their works civilly and morally speaking may be called virtues, and so followed by the double reward of a well-regulated life, both positive (as productive of some temporal good and peace of conscience in this world) and negative (as making their punishment more tolerable), nevertheless (theologically speaking and relatively to God) their works best in form were nothing else than more splendid sins and in the sight of God worthy of no reward
Though the works cannot merit eternal life, they still “civilly and morally may be called virtues.” As to “manner and source (being destitute of the Holy Spirit)” (1.4.10), the works deserve no eternal reward. Only if “internal rectitude of heart and intention of the end” of one’s works are for the true God, may they be “called properly and univocally good works as to the truth of the thing and the mode of operation” (10.5.2). This is not possible for non-Christians. Turretin does acknowledge, however, that “some good can be found in these actions [of the heathen] (as to the external honesty of the act commanded by God and which therefore cannot but be good).”
In an interesting passage, Turretin calls the good actions of the heathen only accidentally sinful: “As the moral actions of the heathen are not sins per se (and as to the substance to the work), but by accident (and to the mode of operation) in the essential conditions” (10.5.6). In other words, the moral actions performed by non-Christian are not in themselves, viz. in relation to the external action itself, sinful. What makes a good action sinful is not the action, but the motive or intention behind it. In an external sense, non-Christians can be called, as Johannes Althusius (1563-1638) said, “just, innocent, and upright.”
Turretin’s perspective on the virtues of the heathen is crucial. According to him (and other Reformed authors such as Althusius, Junius, and Vermigi) it is possible to have an orderly and virtuous pagan community, because external, civil actions are accessible and gathered from nature. “True righteousness,” or “true virtue” (as Augustine called it), is possible only for Christians, but this is only because Christians can meet the necessary internal condition. Externally, a non-Christian community can achieve a degree of virtue. Turretin makes it clear that, given his praise of various pagan authors, civic virtue is not only theoretically possible but to be expected in the pagan world.
The virtue of non-Christians often occasions earthly/temporal rewards, and this is part of the divine purpose. It serves “to teach how much true piety pleases him when he not only remunerates true virtues by eternal reward, but also the images of virtues by temporal blessings not on account of the adherent depravity, but on account of the apparent external good (in order that even unbelievers may have nothing to complain of concerning the justice of God” (10.5.7). So a non-Christian community can be both externally virtuous and externally blessed. True virtues are rewarded eschatologically and are internal. Though Turretin does not say it explicitly, it seem that it is theoretically possible that a community could convert to Christianity and the day-to-day actions of the community remain largely the same. The primary change (apart from the change in external actions related to worship) would be invisible, only visible to God. The intentions change (which cannot be seen) and the reward is eschatological. Though grace is essential for salvation, true virtue, proper worship, and knowledge of the “mysteries of heaven,” it is not necessary for external morality and civil order. Nor is grace necessary for man to reason about virtue and order. Nature contains the resources for virtue and civil order, and reason is sufficient to bring it about.
This explains Turretin’s treatment of political power. He says that the origin of political power is from “God, the Creator,” not God the Redeemer. For this reason, the “political magistrate as such does not serve properly and formally in promoting the kingdom of Christ (18.29.14). For the principle and supreme end of the civil magistrate as such is the glory of God, the Creator…The subordinate end (which regards the community itself) is the public peace and tranquility, the external and temporal good of the state” (18.29.15). The Church alone is the “mediatorial kingdom of Christ.” It is for theses reasons that “political power can be in the hands of heathen and strangers to the covenant” (18.29.14). The magistrate is the leader of the external, civil realm and has no jurisdiction over the internal, spiritual, and mediatorial functions of the church: “Civil power is earthly and natural, reaching only the external man; but ecclesiastical power is spiritual, regarding the internal man and the conscience” (18.29.16). The point is that the external/earthly/civil realm encompasses all external/earthly/civil matters, and the proper conduct in this realm is dictated by God the Creator via nature. Though Christians have a much clearer knowledge of God the Creator through his revelation as the Redeemer, there is nothing exclusively Christian about a virtuous civil realm. The civil realm is not to be redeemed or “Christianized.” This is why the heathen nations “even without a teacher…have learned that God should be worshipped, parents honored, a virtuous life be led and from which as a fountain have flowed so many laws concerning equity and virtue enacted by heathen legislators, drawn from nature itself” (11.1.13). The heathen are competent enough to enact just laws and encourage virtue. On this point, David VanDrunen writes, “In affirming natural law they [i.e., Reformed theologians, including Turretin] professed belief that God had inscribed his moral law on the heart of every person, such that through the testimony of conscience all human beings have knowledge of their basic moral obligations and, in particular, have a universally accessible standard for the development of civil law.”
Turretin on Reason and Philosophy
In Turretin’s comments on reason itself, he is most concerned with establishing the proper boundaries of reason. The issue for Turretin (and, as we will see, with Pictet) is not the legitimacy reason, but the proper boundaries of reason. We must avoid, according to Turretin, two extremes: that of the Socinians, who make reason “the rule of religion and faith” and that of the Lutherans and Roman Catholics, who “attribute little or nothing to it” (1.9.1). Turretin’s position is this: Nothing, either natural or supernatural, can contradict sound reason (contra the Lutherans and Catholics), but supernatural truth need not be proved by reason (contra the Socinians). For example, the Trinity and the incarnation need not be proved by the principle of reason (as arising from its own “storehouse,” as Pictet says), but neither can be true if there is sufficient information showing both to be logically “incompossible.” The Socinians deny the Trinity because it cannot be proved by nature and reason, and the Roman Catholics affirm transubstantiation, despite it being self-contradictory. The former exceed the bounds of reason, for reason cannot be the “first principle from which the doctrines of faith are proved” (1.8.4). If it were, then “it would follow that all religion is natural and demonstrable by natural reason and natural light. Thus nature and grace, natural and supernatural revelation would be confounded” (1.8.5). It confounds God the Creator and God the Redeemer. But, according to Turretin, “The mysteries of faith are beyond the sphere of reason to which the unregenerate man cannot rise” (1.8.5). Turretin is so serious about keeping reason in its place that he declares it a sin to breach them: “[T]he wish to reject mysteries because they cannot be comprehended by reason is a sin not only against faith but also against reason which acknowledges itself to be finite and far inferior to those sublime mysteries” (1.9.6). The latter, i.e., the Catholics belief in transubstantiation, undermines reason. Faith, then, destroys reason. Turretin is careful to safeguard the crucial truth, revelation perfects reason. It does not destroy reason, but complements it. “Light [does not] oppose light, nor truth oppose truth because God is the author of both” (1.9.11).
To make the boundaries more precise, Turretin distinguishes between an “incomprehensible” thing (which cannot be grasped)… [because] we have only an obscure and imperfect knowledge of them” and an “incompossible thing (which cannot be conceived”) (1.9.9). An example of the former is the Trinity and predestination and an example of the latter is transubstantiation. The first principles of reason are also principles in revelation: “For although we do not deny that the mysteries of faith are above reason, still we do not think that they are contrary to it; so that if their truth cannot be proved from reason, still their credibility may be sufficiently established by faith” (19.27.7). Reason’s failure to provide positive support for the mysteries of faith is irrelevant to the truth of the mysteries. But no proposed mystery of faith can contradict the first principles of reason (e.g., the law of non-contradiction). Otherwise, faith destroys reason.
Since the natural knowledge of God is accessible by reason apart from revelation, natural knowledge can come from reason’s own “storehouse.” Hence, civil virtue and various truths concerning God are within the bounds of reason. Again, this natural body of knowledge is insufficient for salvation and true virtue and true righteousness, but it is, nonetheless, real knowledge of God. All of it is accessible by reason as a rule, principle or measure. They can be proved by reason alone. But there are mysteries that cannot be proved by reason. Hence, “Faith is not referred ultimately to reason, so that I ought to believe because I so understand and comprehend; but to the word because God so speaks in the Scriptures” (1.8.5).
On the subject of philosophy in particular, Turretin quickly makes precise distinctions. Addressing the relationship of grace and nature, faith and reason, and supernatural and natural, he writes,
Although every truth cannot be demonstrated by reason (the boundaries of truth being much more widely extended than those of reason), yet no lie against the truth can be sheltered under the protection of true reason, nor can one truth be destroyed by another (although one may transcend and surpass the other) because whatever the one may be—whether below, according to or above reason, and apprehended by the senses, the intellect or faith—it has come from no other source than God, the parent of truth. So grace does not destroy nature, but makes it perfect. Nor does supernatural revelation abrogate the natural, but makes it sure.
This is an excellent summary of the Reformed scholastic view of the relation of reason and revelation. There is perfect harmony between reason and revelation; they complement one another. Though reason cannot demonstrate all truths, sound reason never contradicts truths above reason, and if some proposition of faith contradicts the first principles of reason (e.g., law of non-contradiction), then your proposition is false. Similarly he writes (1.13.13),
Although theology teachers many things that philosophy knows not, it does not follow that a thing may be false in philosophy which is truth in theology because truth is not at variance with truth, nor is light opposed to light. But care must be taken that philosophical truths be not extended beyond their own sphere and the ordinary powers of nature to those things which are of supernatural revelation or power; that the physical be not confounded with the hyperphysical or human with divine things.
As we saw with Calvin, Turretin insists that there is a unity of knowledge in the twofold revelation of God the Creator and God the Redeemer. One does not destroy the other. Together, the self-disclosure of God is made perfect. We should also notice that he continually stresses the importance of the bounds of reason. In his discussion on the “uses” and “abuses” of philosophy his sole concern is keeping philosophy from assuming itself the “office of a master in article of faith, not content with that of a servant” (1.13.6).
Turretin denies that the Apostle Paul, in Colossians 2:8, condemned true philosophy “considered in itself” (1.13.8). He condemned only the vain and false philosophy that “carried [reason] beyond its true bounds and takes upon itself the judgement of supernatural and divine things.” Likewise, Paul did not condemn philosophy in itself in Romans 1:21, 22 and in his disputes with the Athenian philosophers (Acts 17:18).
In conclusion, I summarize some key points. (1) Reason and revelation are not opposed, but are in harmony and complementary. Revelation completes reason and presupposes it. (2) The capacity for reason was not obliterated in the fall. Turretin cites and praises pagan philosophers, and even says that their external moral actions can be called virtuous as to the substance of the action. (3) The civil realm is a realm of natural law. It is not an object of redemption or something to be “Christianized,” though magistrates as magistrates still have an accidental or “extrinsic” role in establishing true religion. (4) Turretin’s greatest (and perhaps only) concern with philosophy is not philosophy itself, but its potential for overreaching into the mysteries of faith and becoming the measure of these mysteries. Reason is not to be the principle by which the truth of the Trinity or the incarnation is measured. Supernatural theology does not need proof from reason, but it cannot in itself contradict sound reason.
See Part 1.
 Turretin admits that non-Christian are able “to know God as merciful by a general mercy tending to some temporal good and the delay of punishment” (1.4.11).
 The essential conditions are that the actions “proceed from a heart purified by faith,” proceed from “internal obedience of the heart,” and are done “done to the glory of God” (1.5.4).
 Johannes Althusius Politica XXI.48. Althusius and Turriten are in agreement on this point: “If the external and civil life of words, deeds and works is accompanied by true faith—together with holiness of thought and desire, and with a right purpose, namely, the glory of God—then it becomes theological. So therefore, when the works of the Decalogue are performed by the Christian to the glory of God because of true faith, they are pleasing to God. But if, to the contrary, they are performed by an infidel or heathen, to whom the Apostle Paul indeed ascribes a natural knowledge of and inclination towards the Decalogue, these works are not able to please God. But in political life even an infidel may be called just, innocent, and upright because of them.”
 Many theologians distinguish between common grace and special grace. Special grace is salvific (so it only pertains to believers) and common grace is for all humankind, regardless of only ultimate standing before God. Common grace would be responsible for civic/earthly virtue and order. See Herman Bavinck’s essay.
 Though magistrates are to support proper worship and suppress heresy, this relates to public order and externals (i.e., “the things without, not things within” (18.29.15)).
 David VanDrunen Natural Law and the Two Kingdoms: A Study in the Development of Reformed Social Thought (Grand Rapids: Eerdmans Publishing Company, 2010), 1. This does not mean that the magistrate, according to Turretin, has no powers related to ecclesiastical realm. But they are related only to externals, not internals. They cannot administer spiritual things, but they can protect the spiritual things from corruption. They have control over “goods and bodies” (18.29.14), but not the conscience.
 Reason is still useful to theology: “In matter of faith reason stands not only in the relation of an instrument by which, but also sometimes from a means and argument from which the theologian argues….Yet we must not from this infer that reason is the principle and rule by which doctrines of faith should be measured” (1.8.8). See his discussion in
 He also writes, “Faith, so far from destroying, on the contrary, borrows [the first principles of nature] from reason and uses them to strengthens its own doctrines” (1.9.5).