“Granting the premisses,” he wrote, “I do not see any escape from Berkeley’s conclusion, that the substance of matter is a metaphysical unknown quantity, of the existence of which there is no proof.  What Berkeley does not seem to have so clearly perceived is that the non-existence of a substance of mind is equally arguable; and that the result of the impartial application of his reasonings is the reduction of the all to co-existences and sequences of phenomena, beneath and beyond which there is nothing cognoscible.”

Hume had written:  “What we call a mind is nothing but a heap or collection of different perceptions, united together by certain relations, and supposed, though falsely, to be endowed with a perfect simplicity and identity.”  Here was mind rejected for the same negative reasons as matter, and Huxley was as ready to point out that while we can know nothing of the

“substance of the thinking thing, we go beyond legitimate reasoning if we therefore deny its existence.” ...  “Hume may be right or wrong, but the most he or anyone else can prove in favour of his conclusions is, that we know nothing more of the mind than that it is a series of perceptions.  Whether there is something in the mind that lies beyond the reach of observation, or whether perceptions themselves are the products of something which can be observed and which is not mind, are questions which can in no wise be settled by direct observation.”

In another passage he writes: 

“To sum up.  If the materialist affirms that the universe and all its phenomena are resolvable into matter and motion, Berkeley replies, True; but what you call matter and motion are known to us only as forms of consciousness; their being is to be conceived or known; and the existence of a state of consciousness, apart from a thinking mind, is a contradiction in terms.  I conceive that this reasoning is irrefragable.  And therefore, if I were obliged to choose between absolute materialism and absolute idealism, I should feel compelled to accept the latter alternative.  Indeed, upon this point Locke does, practically, go as far in the direction of idealism as Berkeley, when he admits that the ’simple ideas which we receive from sensation and reflection are the boundaries of our thoughts, beyond which the mind, whatever efforts it would make, is not able to advance one jot.’”

Locke went further, and Huxley agreed with him.  He declared that the mind cannot “make any discoveries when it would pry into the nature and hidden cause of these ideas.”  We must, in fact, definitely reject what we know as matter as the absolute reality of the universe, for it becomes very plain that what we call matter we know merely as affections of our own consciousness.  In a sense, then, so far as it is opposed to materialism, idealism, according to Huxley, must be the philosophical position of a scientific man.  But the idealism is not the absolute