There seems to be some confusion here concerning authority. I have the authority to say "I like the color green." It would not make sense for me to say "I believe I like the color green" because I have first-hand knowledge concerning my own likes and dislikes and I'm sufficiently confident in my own mental capacities to determine whether or not I'm deceiving myself concerning so simple a matter as my favorite color.

I do not have the authority to say, "Jane likes the color green." I may know Jane quite well, and the probability of my statement being accurate may be quite high, but my saying it is so does not make it so.

You do not cause yourself to like the color green merely by saying that you do. You are describing yourself, but the act of description does not make the description correct. You could speak falsely, but doing so would not change your preferences as to color.

There are some sentence-types that correspond to your concept of "authority." If I accept your offer to create a contract by saying, "we have a contract," I have in fact made is so by speaking. Likewise, "I now pronounce you man and wife." See J.L. Austin's "How to Do Things With Words" for more examples of this. The philosophy of language term for talking like this is that you are making a "performative utterance," because by speaking you are in fact performing an act, rather than merely describing the world.

But our speech conventions do not require us to speak performatively in order to make flat assertions. If it is raining outside, I can say, "it is raining," even though my saying so doesn't make it so. I think the mistake you are making is in assuming that we cannot assert that something is true unless we are 100% confident in our assertion.