In an argument, a good rule of thumb is to only assert statements which your interlocutor is expected to mostly accept (as GDC3 reminds us in another comment). If the statement X won’t be accepted, the statement that “I believe X” may well be accepted, if you are not expected to lie (or be significantly mistaken) about your beliefs. It’s a statement different from X that provides weak evidence about X, and draws attention to X, prompting to think about the possibility of X in greater detail, perhaps raising its probability from obscure to plausible as a result.
Thus, stating “I believe X” is similar to stating “X is somewhat plausible”, in that both communicate weak evidence about X and draw attention to X, allowing to notice its greater plausibility through inference. But stating “X is somewhat plausible” would be a misrepresentation of your understanding of the world if you in fact believe that X is likely (you don’t believe that it’s only “somewhat plausible”), and stating “X is likely” breaks the rule of only asserting statements that will be accepted. Therefore, in this case the best choice is to state “I believe X”, and not “X” or “X is somewhat plausible”.
In an argument, a good rule of thumb is to only assert statements which your interlocutor is expected to mostly accept (as GDC3 reminds us in another comment). If the statement X won’t be accepted, the statement that “I believe X” may well be accepted, if you are not expected to lie (or be significantly mistaken) about your beliefs. It’s a statement different from X that provides weak evidence about X, and draws attention to X, prompting to think about the possibility of X in greater detail, perhaps raising its probability from obscure to plausible as a result.
Thus, stating “I believe X” is similar to stating “X is somewhat plausible”, in that both communicate weak evidence about X and draw attention to X, allowing to notice its greater plausibility through inference. But stating “X is somewhat plausible” would be a misrepresentation of your understanding of the world if you in fact believe that X is likely (you don’t believe that it’s only “somewhat plausible”), and stating “X is likely” breaks the rule of only asserting statements that will be accepted. Therefore, in this case the best choice is to state “I believe X”, and not “X” or “X is somewhat plausible”.