Usual response: whether we have knowledge, for Plato, depends on the object we're asking about. And chairs might be the wrong sort of object to be knowledge-apt. But (apparently) that's a wrong view to have about Plato, since otherwise would be hard to connect knowledge with virtue, which is what Plato wants [Not sure this was the point, but seems to make some sense.]
A real problem: Plato's view has trouble making sense of individual units of knowledge.
Why does Plato think knowledge has to be systematic?
- Because knowledge [recall from end of Theaetetus] connected with explanation--can't know that x without knowing why x: so knowing one thing is knowing two things, and;
- If we know x, we know that we know x.
Apparently this is a pair of distinctions: an internal one (what knowledge is like--which I think is supposed to be the link to explanation) and a second one (knowing that you know--or is this the 'systematic' condition?).
Knowledge and virtue
Possible link between these two via the internal condition on knowledge: knowledge turns out to be a state of soul (the explanatory thing), and virtue is a state of soul, and they turn out equivalent.
Idea that best to view Plato as engaged in exploration (not expostulating a 'secret' doctrine) of the link between virtue and knowledge.
Idea that what the link between knowledge and virtue supposed to establish is that wisdom is the only thing good (in itself).
So we have these questions:
- scope: what sorts of things can we know (e.g. can we know 'boring' things, like that we're sitting in a chair);
- starting question: how do we go from not-knowing to knowing, whatever it is (this was a Theaetetus question).
Note that explanation looks much more holistic than justification. Justification, as we talk about it these days, attaches to individual items of knowledge. Explanation seems to mean a change in your internal structure such that it allows knowledge of much more than an individual x.
Note that might hold this 'holistic' view of knowledge--that only know x when know everything--without being committed to accepting theory of forms. But for Plato knowledge is definitely knowledge of something real, and that (for Plato) is going to commit to commit you to forms.
A 'lingering' question: if knowledge always tells you the right thing to do, it must be that knowledge also tells you the wrong thing to do. But then why is knowledge connected to the right thing to do, rather the wrong thing?