So, Locke is trying to establish somewhat of a hierarchy of language based in clarity. Names of simple substances are closest to the Truth of the substance. "Philosophical" words are furthest from Truth because what the concepts/things they represent are most difficult to nail down. I wonder, then, if we can translate this to exploring the human--do we have a hierarchy of understanding? Or a hierarchy of Truest representation?

While Locke seems to favor the capital T Truth, he here says that nobody is the authority on it.

"Certain and undoubted" brings to mind the classical sense of logos, where it's meaning isn't logic or reasoning (as we tend to think of it now) but is more about the commonly accepted truth. It's a truth that people believe--but that doesn't make it correct. Locke undoubtedly is not intending this meaning but is instead calling for an objective Truth.

Objective knowledge of Truth

Incomplete or inaccurate according to whom? Some objective Truth?

Aaaand there we have it, the rejection of relativism that was also in Locke. "Come, John! There is one Truth and we must seek it out!"

The belief in capital T truth strikes again. For the Greeks, search for Truth was under the purview of the philosophers; here, it's sought by practitioners of science. Interesting parallels between scientists and philosophers.

When there's no Truth (in subjective situations), rhetoric comes to the rescue.

Interesting that there's this call for "proof," some form of evidence, something tangible that we can point to. Such a desire feels very objective, as though there's some Truth this proof will point to. What would such proofs be?