But the truth is we all have it to some degree or other, which is why religious belief is found in every part of the world and every age of history, while rational scepticism is a rare and often lonely stance that leaves Lucretius, Spinoza, Voltaire and Dawkins as heretics. Indeed, the paradox of this realisation is that if belief (in the broad sense of the word) is universal, then no amount of argument can extinguish it, and in a sense therefore, gods really do exist – but inside our heads rather than outside.