Terry: Atheism CONCLUDES (as its very premise) the negation of something (god, gods, deity). How much clearer do I have to be?
But you are confusing definition and how beliefs are actually held. For instance, heliocentrism conclude (or more accurately, postulate) as its very premise that the sun is the center of our solar system.
but a person who subscribe to heliocentrism does so due to evidence, so it would not be accurate at all to say there is anything definitive about heliocentrism.
It would be plain silly to suggest that one could not claim "i am a heliocentrist" and at the same time not be ready to subject heliocentrism to critical evidence-based examination; sure, heliocentrism do postulate (per definition) certain things about the solar system, but believing in heliocentrism is not the same as just having accepted those things "a priori".
But that is exactly the type of claim you make about atheism! Sure, an atheist would say he does not believe in god (at least he would say so in plain language), but there is nothing definitional about that, it is in all cases i can think off a conclusion he has arrived at by examination of evidence and a conclusion he can be swayed from by evidence, just as you can convince me the sun is not the center of the universe by presenting the right type of evidence.