Unlike your saying <"thoughts," with the zero article> , the reason I thought <ones> could be replaced by < those> or <the ones> is because of the article , which is <On the contrary, many of the thoughts>. Then doesn't it matter whether <the> before a noun mentioned before is or not?
No, in this case it does not matter that the noun "thoughts" was mentioned before, and this is because in the subject complement the noun "thoughts" is used to define or describe the "thoughts" in the subject, but does not actually refer to them. It refers to a type of thoughts:
- These thoughts are thoughts that I do not endorse.
Many similar sentences can be written along the same lines:
- These books are books that you should read.
- These ideas are ideas that will not help you.