Well, as already stated, the difficulty arises from an incorrect or incomplete grasp of Greek or Platonic terminology.
The world is generally admitted to exist. If we philosophize about the world, that doesn’t mean that the world is just philosophy or philosophizing, right?
Similarly, perception is generally admitted to exist. If we hypothesize about what it is or how it comes about, it doesn’t mean that perception itself is mere hypothesis.
Now we know that the world exists because we perceive it through our faculties of sensory perception, such as sight.
By sight we mean seeing physical objects. But if we analyze the objects of sight, what we actually see is color, shape, size, distance (between different objects and between objects and ourselves as the perceiving agent), etc.
Color, shape, size, etc., are universals held in common by all objects of sight. They are things we see, not hypotheses. The Forms are similar to these universals though also different in that they are prior to the particulars.
The Ancient Greek word for “see” is
eidon which is the same as Latin
video, “I see”. Greek το εἶδος
to eidos literally means “the seen”, “that which is seen”, or “visible form”, hence English “Form”.
So, Greek “idea” is not the same as English “idea”, it is something that is actually there and that we can see.
If we arrange what we see in ascending order we have:
1. Physical object.
2. Mental object perceived internally.
3. Properties that make up the mental object.
4. Eternal, unchanging “Forms” to which the properties belong.
English “idea” is what we perceive mentally and think about in discursive thought (
dianoia).
Platonic “Idea” (“Form”) is what we see in a kind of non-discursive, intuitive perception (
noesis) or contemplation.
Similarly, English “theory” is just a mental construct. Greek θεωρία,
theoria, is much more than that. It is “contemplation” as in observing something that is seen.
It is somewhat similar to the difference between thinking and lucid dreaming. In lucid dreaming we don’t just think about an object, we actually see it and are perfectly conscious of the fact that we see it as well as of ourselves as the seeing subject.
Edit. So, Socrates often uses hypotheses to prove the validity of a concept, not to deny it. He does this, for example, with the immortality of the soul and concludes that “it turns out that the soul is immortal” (Phaedo 114d). Socrates does not deny the Forms, he merely attempts to find ways of mentally describing or defining them.
For Plato, the Forms are indescribable, eternal realities, that are above discursive thought and can only be referred to in negative terms. For example, this is what the Symposium says about the Form of Beauty:
“It neither comes to be nor perishes, neither waxes nor wanes … nor again will the beautiful appear to him [the philosopher] like a face or hands or any other portion of the body … or piece of knowledge … but itself by itself with itself existing for ever in singularity of form” (211a ff.)
“In that state of life above all others, a man finds it truly worth while to live, as he contemplates essential beauty […] there only will it befall him, as he sees the beautiful through that which makes it visible, to breed not illusions but true examples of virtue, since his contact is not with illusion but with truth” (211d – 212a).
This is not the description of a “hypothesis”, it is the description of a metaphysical reality. We can hypothesize about the Forms but we are always a few steps away from them. We can only experience them in direct metaphysical experience.
It is clear how hypotheses are used in Plato, including in the Phaedo, where Simmias says:
“The argument about recollection and learning, on the other hand, has been provided by means of a hypothesis worthy of acceptance […] and I have accepted that hypothesis on both sufficient and correct grounds” (92d - e).
The hypothesis then, is a provisional thesis adopted to explore its consequences and arrive at a conclusion. Because of the metaphysical nature of the Forms, Socrates does not always come to a definitive definition or conclusion about the Forms even though he comes sufficiently close to point us in the right direction.
Philosophical language was only being developed at the time and no “scientific” definition or description was possible or, indeed, needed as the Forms were meant to ultimately be experienced through a form of perception that can be developed through mental training.
Plotinus gives a more detailed account of the Forms, but ultimately, all we can say in general philosophical terms is that the Forms stand at the threshold between indeterminate and determinate consciousness, where self-aware consciousness begins to perceive things other than itself. The Forms are the underlying patterns that consciousness uses to organize itself in order to produce determinate perception.
Whilst ordinary perception is a cognition arising from mental operations following contact with a sense-object, perception of the Forms arises from activities within consciousness (
nous) itself and independently of sense-objects. Because the Forms stand at the very root of experience, at a stage where the (mental) objects and discursive thought or language related to the objects have not yet emerged, they are impossible to describe. They, nevertheless, are very real. In fact, according to Plato and other Platonists, the Forms are more real than physical reality itself. Like energy particles to physical matter, the Forms are the ultimate constituent elements of subjective experience (i.e., experience directly produced by consciousness) at both cosmic and individual level.