Often a system of philosophy rests on a central claim. The rest of the system is so tightly interwoven with that central claim that changing it changes the system, challenging it challenges the system. The system is like a spider's web: Touch the spider, and the whole web reverberates. The central claim of the logical positivists of early twentieth-century Vienna, and of their immediate successors, was the principle of verification: A sentence of a language was meaningful if and only if it was either analytically true or empirically verifiable. On the basis of such a central claim, a new philosophy was defined; metaphysics was eliminated; a new critique of ethics and theology was propounded; an alternative account of personal identity was suggested; and a fresh view of the nature of logical and mathematical propositions was touted. With the alteration of the principle of verification, the system was altered. When a final successful assault was launched on said principle, the system as a whole tottered. As a consequence, metaphysics began to flourish again.

In Descartes' philosophy, the cogito is the central claim. Consequently, it is quite important to be as clear as possible about the precise nature of this claim. Thus: Is the cogito an argument? Why is this problem so important? Why is it necessary to settle the issue of whether or not the cogito is an argument?