What was the medieval problem of universals?

In medieval Scholasticism, the problem of universals concerned whether "general" things—such as species or attributes—exist independently of the particular objects that exemplify them, and if so, what their nature and relationship to those particulars might be.12

This debate was fueled by the conflicting views of ancient authorities Plato and Aristotle. Four primary schools of thought emerged:12

• Platonic Realism: Affirmed universalia ante rem ("universals before the thing"), arguing that general forms exist independently of particulars.12
• Aristotelian Realism: Affirmed universalia in re ("universals in the thing"), contending that universals exist only as constituents within particular objects.12
• Nominalism: Denied the existence of universals, arguing that reality consists only of particulars and that general terms are merely names or "puffs of sound" (flatus vocis).12
• Conceptualism: Held that universals are mental entities or concepts existing only within individual human minds.12

These disputes were central to medieval philosophy, reflecting a deep engagement with how language and thought relate to the structure of reality.12