Suppose Y to be the imagined first cause and Z to be its effect. Let the letters of the alphabet, _a_, _b_, _c_, _d_, _e_, _f_, _g_, in their order, represent successive moments of time, and let _g_ represent the particular moment at which the effect Z makes its appearance. It follows that the cause Y could not have existed "in its full perfection" during the time _a_--_e_, for if it had, then the effect Z would have come into existence during that time, which, by the hypothesis, it did not do. The cause Y, therefore, must have come into existence at _f_, and if "everything that comes into existence has a cause," Y must have had a cause X operating at _e_; X, a cause W operating at _d_; and, so on, _ad infinitum_.[31] If the only demonstrative argument for the existence of a Deity, which Hume advances, thus, literally, "goes to water" in the solvent of his philosophy, the reasoning from the evidence of design does not fare much better. If Hume really knew of any valid reply to Philo's arguments in the following passages of the _Dialogues_, he has dealt unfairly by the leader in concealing it:-- "But because I know you are not much swayed by names and authorities, I shall endeavour to show you, a little more distinctly, the inconveniences of that Anthropomorphism, which you have embraced; and shall prove, that there is no ground to suppose a plan of the world to be formed in the Divine mind, consisting of distinct ideas, differently arranged, in the same manner as an architect forms in his head the plan of a house which he intends to execute. "It is not easy, I own, to see what is gained by this supposition, whether we judge the matter by _Reason_ or by _Experience_. We are still obliged to mount higher, in order to find the cause of this cause, which you had assigned as satisfactory and conclusive. "If _Reason_ (I mean abstract reason, derived from inquiries _a priori_) be not alike mute with regard to all questions concerning cause and effect, this sentence at least it will venture to pronounce: That a mental world, or universe of ideas, requires a cause as much as does a material world, or universe of objects; and, if similar in its arrangement, must require a similar cause. For what is there in this subject, which should occasion a different conclusion or inference? In an abstract view, they are entirely alike; and no difficulty attends the one supposition, which is not common to both of them.