Formal:
* Assertion: This is a strong, confident statement of belief.
* Claim: This is a statement that is put forward as a fact, but may not be proven.
* Proposition: This is a statement that can be either true or false.
* Opinion: This is a personal view or belief, often subjective.
* Belief: This is a conviction or acceptance of something as true.
Informal:
* Thought: This is a simple way to refer to what someone is thinking.
* Idea: This is a concept or suggestion.
* Feeling: This describes an emotional response to something.
* Viewpoint: This is a perspective or angle on a particular issue.
* Perspective: Similar to viewpoint, this emphasizes how someone sees a situation.
The best term to use will depend on the specific context and what you want to emphasize. For example, if you want to emphasize that the statement is based on evidence, you might use the word "assertion." If you want to emphasize that the statement is a personal opinion, you might use the word "belief" or "viewpoint."