Are there philosophical or cognitive theories about "creating truth by defining"?
Particularly, I refer to a phenomenon of saying something and then having it become true, because of how it's said.
It's a bit like "pure a prioric reasoning", but since there are also valid a prioric reasonings that also have broader than a priorical truths (e.g. mathematics), then this is not exactly it. Rather, "creating truth by definition" would be to formulate premises from scratch and then have them become truths by some other means than "tying them to natural sciences" for example.
Particularly, this phenomenon makes it possible to create "plausible theories" and "plausible premises" out of nothing and then have them appear valid, because of their plausibility, believability etc. If these touch contexts that are uncertain or out of which absolute truth cannot be found, then these might also be interpreted as "as true as there can be".