The theory suggests that the physical world is not as real or true as “Forms”. According to this theory, Forms—conventionally capitalized and also commonly translated as “Ideas”—are the non-physical, timeless, absolute, and unchangeable essences of all things, of which objects and matter in the physical world are merely imitations.
The pre-Socratic philosophers, starting with Thales, noted that appearances change, and began to ask what the thing that changes “really” is. The answer was substance, which stands under the changes and is the actually existing thing being seen.
The Forms are expounded upon in Plato’s dialogues and general speech, in that every object or quality in reality—dogs, human beings, mountains, colors, courage, love, and goodness—has a form. Form answers the question, “What is that?” Plato was going a step further and asking what Form itself is. He supposed that the object was essentially or “really” the Form and that the phenomena were mere shadows mimicking the Form; that is, momentary portrayals of the Form under different circumstances.
Plato’s Socrates held that the world of Forms is transcendent to our own world (the world of substances) and also is the essential basis of reality. Super-ordinate to matter, Forms are the most pure of all things. Furthermore, he believed that true knowledge/intelligence is the ability to grasp the world of Forms with one’s mind.