Berkeley's focus in the first dialogue of Mind and Its Objects is on metaphysics and logic. The core argument of the dialogue is the distinction that Hylas insists on between what exists and what is perceived (260) as existing. sThe perception of the thing cannot be divided from the existence of the thing as far as human experience is concerned. Where division occurs is where contradiction surfaces because the existence of what cannot be directly perceived by human sensibilities cannot be definitively guaranteed.
The human mental experience of perceiving is therefore the primary reality. Perception of material reality is inseparable from and fused with human imagination. The sense perception of the idea or the thing may be as far as the human mind can go, but that in Berkeley's view does not prove that the mind exists or that the objects of mental perception or indeed their attributes exist independently of it. Indeed, through Hylas Berkeley takes the view that the proof cannot be made, even when such obvious attributes as fire, pain, and heat, or wormwood and bitter taste are so enmeshed: "those qualities, as perceived by us, are pleasures or pains; but not as existing in the external objects" (Berkeley 264). Nonsentient objects or beings cannot claim their own attributes. Rather, it is human perception that assigns such attributes. Berkeley eventually includes material extension, shape, and motion, which are inconceivable when abstracted from sense perception. Through Philonous Berkeley articulates the inescapable logic of such an assertion:
If it be allowed that no idea nor anything like an idea can exist in an unperceiving substance, then surely it follows that no figure or mode of extension, which we can either perceive or imagine, or have any idea of, can be really inherent in Matter; not to mention the peculiar difficulty there must be in conceiving a material substance, prior to and distinct from extension, to be the subs...