Refuting a claim is showing it to be false--typically by producing reasons that make it clear that it's false. Until you produce reasons, you may deny or reject the claim, but you won't have refuted it.

In addition, don't say:

Berkeley refutes Locke's claim that there are material objects.

unless you think that Berkeley has succeeded in demonstrating that Locke's claim is false. If Berkeley has refuted Locke, then Locke must be wrong. You can't write: "Berkeley refuted Locke's claim, but in fact Locke was right."

If you doubt whether Berkeley's criticisms of Locke are successful, you should say instead:

Berkeley denies Locke's claim that...

or:

Berkeley argues against Locke's claim that...

or:

Berkeley rejects Locke's claim that...

or:

Berkeley tries to refute Locke's claim that...

Similarly, you should not say that Locke has proven some claim, or shown that something is the case, unless you think that Locke's arguments for his claim are successful. If Locke has proven a claim, then the claim must be true.

If you doubt whether Locke's arguments for a claim are successful, then you should say instead:

Locke argues that...

or:

Locke defends the claim that...

or:

Locke tries to prove that...

or something of that sort.