I think there is a causal link between nominalistic epistemology and voluntarism. Nominalism/conceptualism consider ideas in our minds as the source of concepts rather then real essences in things in the world outside our minds, as moderate realism believes. Voluntarism is the philosophical doctrine that the will is a fundamental or dominant factor in the individual’s sentient powers. I think this doctrine came from a percieved reduction in the range of reason which began with nominalist and conceptualist epistemology. Moderate realism believes humans know universal essences from an immaterial intellectual power in the soul. The first act of this intellectual power of the mindis abstraction where universal concepts are abstracted from sense objects recieved from particular material things outside our minds in the real world. This is followed by the 2nd and 3rd acts of the mind using these universal concepts in acts of reasoning. This is the basis of logic and argumentation.
Nominalism denies the existence of universal concepts by which we know real essences. Nominalism believes particular things have no essential form in them. They are just collections of things we assign names to. The growth of nominalist philosophical and therefore theological views led to a denial of middle of the road epistemology, moderate realism. This resulted in the widespread denial of realist metaphysics. Realist metaphysics asserts that change is real in the world, that there are such things as potentiality and actuality of things that can reach natural potential in acts according to their teleological potential . Actuality is the act of existence of potential powers in the nature of a thing. In humans this includes the physical, mental and spiritual growth of humans. The actualization of human nature results in a higher level of goodness, beauty and truth present in human beings. Metaphysical realities are transcendental qualities of a thing such as goodness, beauty, truth and result from the four cause of things (final, formal, efficient and effective causes).
Voluntarism rose when the role of the intellect in human decision making was lowered by nominalist beliefs and rejection of realist metaphysics leaving the will to be being concieved as the higher power. One of the most extreme examples of this is Nietzche’s will to power, which was an important principle of his approach to governing the world.
In these days, there is a humanism which has become a religion of humanity. It demands a false moralism believing there is nothing higher than material processes in the potentiality of a human being. This humanism denials the existence of final and formal causes in material things. It denies that man has a real human nature and essence that has teleology. It denies that agents act toward their natural ends. It says humans have no nature or natural ends and purpose. This leaves the intellect as a severely limited power unable to understand and recognize the four causes in nature itself. This is a crisis in natural philosophy and a limitation of science to only empirically based knowledge, which is tentative itself. It has led to a scientism that limits the range of true science, but that is another subject even thouigh it is related to the subject here.
If like nominalism, we are to believe there is no real essence in things, then this would lead to the belief that humans are just animals. In this idea, the human animals are only groups of particulars having different characteristics. Some are more physically beautiful, more intelligent, stronger, etc. and thus of more worth in a utilitarian sense. The dignity of the human person has its source in our real essence and nature which has both a soul and body. It is both material and spiritual in its potentiality of powers. Our intellect has spiritual powers to know and understand real universal concepts and truths. There is truth in logical principles such as the principle of non-contradiction, the principle of finality and the four causes of things. The existence of real essences is the source of human equality. The soul is the form of our body. We are in the soul, not the other way around. If we don’t understand our real common essences as the basis for human nature, we end up with a philosophy of human inequality.
The social contract of John Locke is not enough to ensure our equal human dignity. The social contract theory is a false human construct subject because it has no basis in human nature and is subject to the views of those in power including governments and dictators. Instead our human dignity and equality is based in our human nature, an existing reality with teleological principles that apply.
Thus in modern times, we are left with a voluntaristic approach to philosophy, a relativistic approach to epistemology and the denial of metaphysical realities found in objective goodness, beauty and truth. This trend has continued into modern age philosophy and theology resulting in many philosophical and theological errors passed on into our times causing a rise of atheistic humanism and a decline in morals and wisdom about human nature in cultures throughout much of the world. Relativism and voluntarism have increased like a pendulum swinging to an extreme. Let us hope for a revival of moderate realism in our time.