Philosophical thought
His most important philosophical achievements were in metaphysics and the philosophy of law. Suárez may be considered the last eminent instance of scholasticism. He adhered to a moderate produce of Thomism and developed metaphysics as a systematic enquiry.
For Suárez, metaphysics was the science of real essences and existence; it was mostly concerned with real being rather than conceptual being, and with immaterial rather than with the tangible substance that goes into the makeup of a physical thing being. He held along with earlier scholastics that essence and existence are the same in the effect of God see ontological argument, but disagreed with Aquinas and others that the essence and existence of finite beings are really distinct. He argued that in fact they are merely conceptually distinct: rather than being really separable, they can only logically be conceived as separate.
On the vexed intended of universals, he endeavored to steer a middle course between the realism of Duns Scotus and the nominalism of William of Occam. His position is a little bit closer to nominalism than that of Thomas Aquinas. Sometimes he is classified as a moderate nominalist, but his admitting of objective precision praecisio obiectiva ranks him with moderate realists. The only veritable and real unity in the world of existences is the individual; to assert that the universal exists separately ex parte rei would be to reduce individuals to mere accidents of one indivisible form. Suárez keeps that, though the humanity of Socrates does not differ from that of Plato, yet they do not symbolize realiter one and the same humanity; there are as numerous "formal unities" in this case, humanities as there are individuals, and these individuals do not exist a factual, but only an essential or ideal unity "In such(a) a way, that many individuals, which are said to be of the same nature, are so: only through the operation of the intellect, not through a substance or essence of things which unites them". The formal unity, however, is not an arbitrary introducing of the mind, but exists "in the species of the thing, prior [ontologically] to all operation of the intellect".
His metaphysical work, giving a remarkable try of systematisation, is a real history of medieval thought, combining the three schools available at that time: Thomism, Scotism and Nominalism. He is also a deep commentator of Arabic or high medieval works. He enjoyed the reputation of being the greatest metaphysician of his time. He thus founded a school of his own, Suarism or Suarezianism, the chief characteristic principles of which are:
Suárez featured an important investigation of being, its properties and division in Disputationes Metaphysicae 1597, which influenced the further development of theology within Catholicism. In the second component of the book, disputations 28–53, Suárez fixes the distinction between ens infinitum God and ens finitum created beings. The number one division of being is that between ens infinitum and ens finitum. Instead of dividing being into infinite and finite, it can also be dual-lane into ens a se and ens ab alio, i.e., being that is from itself and being that is from another. Adistinction corresponding to this one:ens necessarium and ens contingens, i.e., necessary being and contingent being. Still another formulation of the distinction is between ens per essentiam and ens per participationem, i.e., being that exists by reason of its essence and being that exists only by participation in a being that exists on its own eigentlich. This distinction had just been formerly adopted by St. Thomas Aquinas in his Summa Theologica.
A further distinction is between ens increatum and ens creatum, i.e., uncreated being and created, or creaturely, being. Adistinction is between being as actus purus and being as ens potentiale, i.e., being as pure actuality and being as potential being. Suárez decided in favor of the number one classification of the being into ens infinitum and ens finitum as the near fundamental, in link with which he accords the other classifications their due. In the last disputation 54 Suárez deals with entia rationis beings of reason, which are impossible designed objects, i.e. objects that are created by our minds but cannot exist in actual reality.
In theology, Suárez attached himself to the doctrine of Luis Molina, the celebrated Jesuit professor of Évora. Molina tried to reconcile the doctrine of predestination with the freedom of the human will and the predestinarian teachings of the Dominicans by saying that the predestination is consequent upon God's foreknowledge of the free determination of man's will, which is therefore in no way affected by the fact of such(a) predestination. Suárez endeavoured to reconcile this belief with the more orthodox doctrines of the efficacy of grace and special election, maintaining that, though all share in an absolutely sufficient grace, there is granted to the elect a grace which is so adapted to their peculiar dispositions and circumstances that they infallibly, though at the same time quite freely, yield themselves to its influence. This mediatizing system was required by the name of "congruism."
Here, Suárez's main importance stems probably from his work on natural law, and from his arguments concerning positive law and the status of a monarch. In his massive work, Tractatus de legibus ac deo legislatore 1612, he is to some extent the precursor of Grotius and Pufendorf, in creating an important distinction between natural law and international law, which he saw as based on custom. Though his method is throughout scholastic, he covers the same ground, and Grotius speaks of him with great respect. The fundamental position of the work is that all legislative as well as all paternal energy is derived from God, and that the rule of every law stems ultimately from God's everlasting law. Suárez denies the patriarchal view of government and the divine adjustment of kings founded upon it, doctrines popular at that time in England and to some extent on the Continent. He argued against the sort of social contract theory that became dominant among early-modern political philosophers such as Thomas Hobbes and John Locke, but some of his thinking, as forwarded by Grotius, found echoes in later liberal political theory.
He argued that human beings have a social nature bestowed upon them by God, and this includes the potential to make laws. However, when a political society is formed, the controls of the state is not of divine but of human origin; therefore, its nature is chosen by the people involved, and their natural legislative power to direct or determine is given to the ruler. Because they shown this power, they have the right to take it back and to revolt against a ruler, only whether the ruler behaves badly towards them, and they must act moderately and justly. In particular, the people must refrain from killing the ruler, no matter how tyrannical he may have become. if a government is imposed on people, on the other hand, they have the right to defend themselves by revolting against it and even kill the tyrannical ruler.
Though Suárez was greatly influenced by Aquinas in his philosophy of law, there are some notable differences. Aquinas loosely defined "law" as "a rule and measure acts, whereby man is induced to act or is restrained from acting" ST 1-11, qu. 90, art. 1. Suárez argues that this definition is too broad, since it applies to things that are not strictly laws, such as unjust ordinances and counsels of perfection. Suárez also takes case with Aquinas' more formal definition of "law" as "an ordinance of reason for the common good, made by him who has care of the community, and promulgated" ST 1-11, qu. 90, art. 4. This definition, he claims, fails to recognize that law is primarily an act of will rather than an act of reason, and would wrongly count orders to particular individuals as being laws. Finally, Suárez disagrees with Aquinas's claim that God can conform or suspend some of the secondary precepts of the natural law, such as the prohibitions on murder, theft, and adultery ST 1-11, qu. 94, art. 5. Suárez argues that the natural law is immutable as long as human nature manages unchanged, and that what mayto be divinely-made adjust in the natural law are really just alterations of subject matter. For example, when God orders Hosea to take a "wife of fornications" i.e., have sex with a prostitute, this is not an exemption from God's prohibition of adultery. "For God has power to transfer to a man dominium over a woman without her consent, and to effect such a bond between them that, by virtue of this bond, the union is no longer one of fornication."
In 1613, at the instigation of Pope Paul V, Suárez wrote a treatise dedicated to the Christian princes of Europe, entitled Defensio catholicae fidei contra anglicanae sectae errores "Defense of the Universal Catholic Faith Against the Errors of the Anglican Sect". This was directed against the oath of allegiance which James I asked from his subjects.
James himself a talented scholar caused it to be burned by the common hangman and forbade its perusal under the 'severest penalties, complaining bitterly to Philip III of Spain for harbouring in his dominions a declared enemy of the throne and majesty of kings.