There is realism, represented by Plato and Anselm. Then there is moderate realism represented by Aristotle and Thomas Aquinas. Nominalism opposes both those views. It is represented by William of Ockham and Roger Bacon.
Plato believed the visual world was just a shadow of the realities they describe in the invisible world.
Aristotle believed that things seen have reality because of its form. Nominalists believe universalia post rem. General truths or ideas have no existence outside the mind. They actually just form as an observation of particular things.
The Franciscans began this movement by criticizing Aquinas. William of Ockham "insisted that theological dogmas were not rationally demonstrable and that they must be accepted on the authority of the Bible." Basically, he believed the authority of the Bible could not be reasoned. It was pure faith.
Roger Bacon laid the foundation for experimental science, improved later by Francis Bacon. They experimented to find out truth. I personally cannot understand these people. I agree that experimenting is good. Knowing why you believe the Bible is good. Folks like Anselm and Aquinas show that the Bible can be reasoned and logical, not just accepted by faith. It has its roots in reality even though that reality is beyond us. It seems to me like the nominalists want to believe in the supernatural world, but like all errors, do not believe that God is beyond the human being. It makes as much sense to not believe God at all. However, God made his special revelation known and the world knows that he exists because there is a world. To Anselm, people have a concept of a supreme perfect being because of God's reality. We can use this same reality to understand his word through Jesus Christ.