Essay phrases to avoid repetition

Could somebody suggest synonymous phrases/words that could be used instead of “support one’s claims”, “the author furthers his line of argumentation”, “find credence with one’s words” and “builds his argumentation”, which are often used in the sample essays to avoid repetition that essentially convey the same idea?

@Vintagey here are a few ideas (I’m sure there are more):

*gives/provides/establishes evidence
*substantiates
*verifies
*proves (however I would be careful when using this word, since providing evidence is often not the same as proving something)

The author also says, …