Book VI continues with more fine distinctions. Unhelpfully translations differ, and you really need to know which Greek concept is being put in play. For example, the one we've been using wants to talk about "deliberation."
There is a difference between inquiry and deliberation; for deliberation is inquiry into a particular kind of thing. We must grasp the nature of excellence in deliberation as well whether it is a form of scientific knowledge, or opinion, or skill in conjecture, or some other kind of thing.
You will recall that we already discussed deliberation separately in III.2-3. The translation's use of the term here is ambiguous; the concept Aristotle was discussing in Book III was prohairesis but here it is phronesis, the latter of which began to discuss the other day. If any of you are reading the Irwin translation, he tries to keep the English words he uses linked carefully to the Greek words, but even then you'll see him talk of "inquiry" versus "deliberation" versus "intelligence" versus "wisdom."
Following this section exactly may not be possible on the first pass. These are intricate distinctions about invisible mental faculties, originally in ancient Greek and now in several English translations. If you really want to map this down, it will take a little time.
Scientific knowledge it is not; for men do not inquire about the things they know about, but good deliberation is a kind of deliberation, and he who deliberates inquires and calculates. Nor is it skill in conjecture; for this both involves no reasoning and is something that is quick in its operation, while men deliberate a long time, and they say that one should carry out quickly the conclusions of one's deliberation, but should deliberate slowly.
Irwin translates what they are giving as "it is not skill in conjecture" instead as that intelligence "is not good guessing." The problem with even very good guessing is that you could go wrong; what Aristotle is looking for from phronesis is a little more security that you'll choose your actions correctly.
Again, readiness of mind is different from excellence in deliberation; it is a sort of skill in conjecture. Nor again is excellence in deliberation opinion of any sort. But since the man who deliberates badly makes a mistake, while he who deliberates well does so correctly, excellence in deliberation is clearly a kind of correctness, but neither of knowledge nor of opinion; for there is no such thing as correctness of knowledge (since there is no such thing as error of knowledge)...
"There is no such thing as correctness of knowledge" and "there is no such thing as error of knowledge" both sound very suspicious to contemporary readers. You have to know that Aristotle's definition of knowledge assumes truth: knowledge, per the Posterior Analytics, is "Justified true belief." Thus, your knowledge can't be in error because it would then not be true, and if it's a false belief it wasn't knowledge to begin with.
So, just as he wants phronesis to be more secure than 'good guessing,' he defines knowledge to be safely true.
Socrates was aware of this theory of knowledge and had rejected it (at least in Plato's telling), but Aristotle found it satisfactory. This account of knowledge held up a very long time. It was not until the late 20th century that a serious problem was found with it (though the Wikipedia article does give some earlier examples of people asking questions about it). In 1963 kind of a fun challenge was raised by Edmund Gettier, which nobody has yet figured out how to solve. Actually, epistemology is a lot of fun all the way around. Nothing very serious hangs on it (except for little things like knowledge and truth), and it's a great deal of fun to think about.