Locke next inquired to what extent knowledge - in the way either of intuitive certainty, demonstrative certainty, or sense perception - is possible, in regard to each of the four (already mentioned) sorts of knowable relation.
The cardinal assumption of Plato's metaphysic is, that the real is definitely thinkable and knowable in proportion as it is real; so that the further the mind advances in abstraction from sensible particulars and apprehension of real being, the more definite and clear its thought becomes.
The development of particular things from this germinal matter consists in differentiation, the acquiring of particular forms of which the knowable universe consists (cf.
These are all knowable things, and yet there is not universal agreement on them.
If everything knowable is an example of evolution, and evolution is by definition a transformation of matter and motion, then everything knowable is an example of a transformation of matter and motion.
It appears, therefore, that Spencer ultimately describes the Knowable in terms of the mechanical conceptions of matter and motion, and that this must give a materialistic colouring to his philosophy.
The second sort of knowable relation is sometimes intuitively and sometimes demonstrably discernible.
On the contrary, his contention is that of Fechner - that all knowable things are inner psychical realities beneath outer physical appearances - the invisible symbolized by the visible.
Nevertheless, as he believes all the time that everything knowable throughout the whole world of evolution is phenomena in the sense of subjective affections of consciousness, and as he applies Hume's distinction of impressions and ideas as a distinction of vivid and faint states of consciousness to the distinction of ego and non-ego, spirit and matter, inner and outer phenomena, his philosophy of the world as knowable remains within the limits of phenomenalism.
But, in spite of these materialistic tendencies, he followed Hume in reducing matter and everything knowable to phenomena of consciousness; and, supposing that nothing is knowable beyond phenomena, concluded that we can neither affirm nor deny that anything exists beyond, but ought to take up an attitude which the ancient sceptics called Aphasia, but he dubbed by the new name of Agnosticism.