Implicit atheism and explicit atheism are types of atheism. In George H. Smith's Atheism: The Case Against God, "implicit atheism" is defined as "the absence of theistic belief without a conscious rejection of it", while "explicit atheism" is "the absence of theistic belief due to a conscious rejection of it". Explicit atheists have considered the idea of deities and have rejected belief that any exist. Implicit atheists, though they do not themselves maintain a belief in a god or gods, have not rejected the notion or have not considered it further.