Nominalism and realism are what opposes each other. The difference between them is great. Understanding both of these makes it possible to look at familiar things a little differently. The debate about which theory is correct is centuries old. Many leading philosophers took part in it. Each expressed his opinion, based on the work of earlier thinkers.
Realism and nominalism are opposing directions of medieval scholastic philosophy. Supporters of nominalism tried to prove that there are only single things, and supporters of realism were convinced that everything exists in the divine mind. Extreme nominalists argued that general concepts are the result of abstraction, which is connected with thinking, extreme realists claimed that general concepts are universals that exist independently of us - they were even before the appearance of things.
Nominalism and realism in medieval philosophy were very different from each other, were in a state of contradiction. The discussions that arose between the parties led to the emergence and development of a certain logic, which significantly influenced the development of scholasticism. Also, nominalism and realism, or rather disputes related to them, led to the development of scientific rigor, influenced the theory of sets. The polemic of nominalism and realism lasted several centuries.
Realism of the Middle Ages is a doctrine in which it is stated that only universals (that is, general concepts) possess reality. Moreover, things themselves are temporary, isolated and constantly changing. Concepts are the root cause of things - they originated from the divine mind.
In nominalism, the emphasis is placed on the fact that the will prevails over the mind. There are no concepts in the divine mind. The will of God was aimed at the creation of things, but concepts are the creation of knowing souls.
Thomas Aquinas tried to overcome both extremes. In response to the nominalists, he said that the concepts that appeared by the will of the divine mind are prototypes of the concepts that we have now. He argued to realists that those concepts that are formed in the human mind are secondary to the basic essence of things.
Thomas Aquinas argued that cognition is based on the fact that a person is affected by two sides at once: the intelligible and the sensual. The thing is that objects lead a peculiar double existence: inside the human consciousness, as well as outside it. Sensual species give people the opportunity to understand the individual in things. Philosophical knowledge of things elevates man, brings him closer to God.
Nominalism and realism later began to be considered somewhat differently. Using knowledge of things, thinkers tried to answer questions related to the existence of things, its causes, fundamentals, and also meaning. Many believed that it is through things that one can comprehend reality.
Realism as a direction of scholasticism is a doctrine in which it is stated that true reality is connected only with universals, and individual objects have nothing to do with it. The place of existence of such objects is the empirical world. One can speak of real being only in relation to things with constancy, which are eternal. Universals are thoughts originating from the divine mind.
In nominalism, the existence of general concepts was not allowed. Universals - this is what came after things. General concepts are only names that cannot have an independent existence at all.
Nominalism and realism is a debate about how the transactional and the general interact. Of course, in realism a lot of idealism, and in nominalism - from materialism.