Shelley’s belief in a god in The Necessity of Atheism was nonexistent. He believed there was an explanation for everything that happened in the human existence. The knowledge one had was all that was needed have a good life. There were three degrees of excitement one needed to have a complete life without belief in god. He explained “The evidence of the senses,” “reason,” and “testimony” are all the ways in which he could prove there was no god:
From this it is evident that having no proofs from any of the three sources of conviction: the mind cannot believe the existence of a God, it is also evident that as belief is a passion of the mind, no degree of criminality can be attached to disbelief, they only are reprehensible who willingly neglect to remove the false medium thro' which their mind views the subject. It is almost unnecessary to observe, that the general knowledge of the deficiency of such proof, cannot be prejudicial to society: Truth has always been found to promote the best interests of mankind. Every reflecting mind must allow that there is no proof of the existence of a Deity (Forman).
Shelley writes, “The senses are the source of all knowledge to the mind, consequently their evidence claims the strongest assent” (Forman).