Although many atheist philosophers have offered arguments against the existence of God, some have thought that it is not necessary to do so in order to establish the rationality of atheism. There is, it is argued, a presumption of atheism; because of the nature of theism, we ought to be atheists unless we are presented with strong evidence for theism, even if we do not have any specific arguments for atheism.

There are two types of atheism: weak and strong. Weak atheism is defined negatively as the absence of belief in God. Strong atheism is defined positively as the belief that God does not exist.

The presumption of atheism argument comes in two forms, one relating to weak atheism and the other to strong atheism.

The Presumption of Weak Atheism

Some weak atheists argue that atheism is the default position because he who asserts must prove. Theists make the positive claim that God exists. Weak atheists do not make the positive claim that God does not exist, but merely withhold their assent from the theists‘ claim that God does exist. According to the weak atheist, because it is the theist that makes an assertion, it is the theist that bears the burden of proof. He who asserts must prove, and so unless the theist can offer some convincing argument for God’s existence, the weak atheist will be justified in his atheism.

The Presumption of Strong Atheism

The same argument does not apply to the strong atheist. The strong atheist’s position is just as assertive as that of the theist. The theist asserts that God exists; the strong atheist asserts that God does not exist. In the hands of the strong atheist, the presumption of atheism argument must therefore be reformulated. The strong atheist cannot point to the tentativeness of his position as a reason why he need not offer an argument for it. Instead, some strong atheists point to the ordinariness of their position as fulfilling this role.

Strong atheism, it is argued, coheres with our observations of the world around us; it does not go beyond our experiences. Theism, on the other hand, makes extraordinary claims about spiritual beings, a heavenly realm, and the imminent resurrection of the dead. These claims, unlike those of the strong atheist, are extraordinary, i.e. they do not fit with our everyday experiences, and they are therefore to be disbelieved except in the face of extraordinary evidence.