This concept is implausible if there is a just and loving God, but if some evil genius had created the world instead -- along with human understanding of God -- then every single belief could be brought into doubt. Essentially, Descartes takes the null hypothesis regarding mental interpretations of the external world. Still, this construction of absolute doubt is merely a portion of Descartes' argument, because he intends to find some undeniable truth -- a principle beyond doubt -- which can destroy the premise that nothing can be known. In his Meditations he words this as "I am, I exist." This statement -- at other times worded as 'I think, therefore I am' -- is accepted by Descartes because even a maniacal construction of the world could not disprove his own existence, since he believes himself to exist. Obviously, this argument depends upon some distinction between the subjective and the objective. Put differently, Descartes utilizes internal reflection to solidify some universal existence. The clear consequence of Descartes rejection of the null hypothesis of existence is that the human being, to him, is intrinsically a thinking entity: its function is to think. Therefore, even though his reasoning suggests existence, this existence is immaterial; the defining aspect of the human being is the mind -- which is Descartes' modern formulation of the Christian conception of the soul. So the mind is necessarily distinct form the vegetative requirements of the body -- food, water, ect. -- as a result of the "truth" Descartes uses to break universal skepticism. Additionally, all aspects of human perception must then be relegated into one of these two tiers of the individual: higher thought, or animalistic impressions. Basically, Descartes uses his mental identity as the launching pad for Cartesian Dualism and as the bedrock for the knowledge of universals.

This, according to Clifford, is absolutely unacceptable. From Clifford's first example, if the shipowner possesses reasons to believe in an all-powerful, wholly good God, he also possesses...

After all, if we are inclined to accept Descartes' notion of existence, then this existence is an intrinsic moral good; therefore, whoever or whatever created life, did so as an act of goodness. This is precisely the line of reasoning that Clifford uses to arrive at the conclusion that it is always wrong to accept claims based upon faith. Descartes, on the other hand, would contend that it is not faith that allows an individual to arrive at the conclusion that a morally just and all-powerful God exists -- reasoning tells us this.
The distinction is that Clifford believes we should always and in every case rely upon empirical evidence to tell us the truth or falsity of features of the external world; and these remain the only tools with which we are charged with the task of making moral decisions in this world. Descartes suggests that our senses can be deceiving and that the elemental truths of our existence are immaterial in nature and, as a result, only possess an abstract existence in our minds. Taken together, an individual would be incapable of making decisions in the real world if they believed both in empirical reasoning and in the notion that abstract doubt is capable of toppling claims about the physical world. Fundamentally, this is because empirical observations operate under the assumption that what we see, hear, feel, taste, and smell are facets of the real world -- they are concrete. However, they are also discrete. They are simply a set of observations, with which we inductively decide to arrive at universal conclusions. As such, there is always some level of doubt -- even if these conclusions are unassailable from a rationalistic stance. So, applying Descartes' method of doubt to Clifford's method of proof results in complete and utter skepticism.

Reference:

Cahn, Steven M. And Maureen Eckert. 2006. Philosophical Horizons: Introductory Readings. California: Thomson and Wadsworth.