To affirm positively or assert as fact is to do what?

The term that means to affirm positively or assert as fact is "aver." In legal and formal contexts, to aver is to state something to be true, often in a confident and authoritative manner. It is commonly used to denote a declaration that is made with certainty, implying that the person making the statement believes it to be factual and is asserting it as such.

While "validate," "attest," and "contend" have their own nuanced meanings, they do not specifically convey the same straightforward assertion of fact that "aver" does. "Validate" refers more to the act of confirming or making something valid, "attest" involves witnessing or providing evidence for a statement, and "contend" implies arguing or asserting a point in a debate or dispute. None of these alternatives emphasize the direct affirmation of truth in the same way that "aver" does.