154. Such a doctrine--a doctrine founded on the testimony of the senses, which ends by showing that the senses testify to nothing--cannot be criticised step by step according to the order in which its author puts it, for its characteristic is that, in order to state itself, it has to take for granted popular notions which it afterwards shows to be unmeaning. Its power over ordinary thinkers lies just in this, that it arrives at its destructive result by means of propositions which every one believes, but to the validity of which its result is really fatal. An account of our primitive consciousness, which derives its plausibility from availing itself of the conceptions of cause and substance, is the basis of the argument which reduces these conceptions to words misunderstood. It cannot, therefore, be treated by itself, as it stands in the first part of the Treatise on the Understanding, but must be taken in connection with Part IV., especially with the section on ‘Scepticism with regard to the Senses;’ not upon the plan of discrediting a principle by reference to the ‘dangerous’ nature of its consequences, but because the final doctrine brings out the inconsistencies lurking in that assumed to begin with. On this side of his scepticism Hume mainly followed the orthodox Berkeley, of whose criticism of Locke, made with a very different purpose, some account must first be given. The connection between the two authors is instructive in many ways; not least as showing that when the most pious theological purpose expresses itself in a doctrine resting on an inadequate philosophical principle, it is the principle and not the purpose that will regulate the permanent effect of the doctrine. Berkeley’s religious interest in making Locke consistent.