He hazards the general statement, because he assumes (sometimes without knowing that he does so) that nature is uniform and constant, that it will do to-day as it did yesterday, and does in infinite space as it does in the visible universe.
The knowledge that is possible to the empiricist, then, is merely that which is derived from direct experience, and simple summations or generalisations into a single assertion of a number of similar assertions, all of which were individually derived from experience.

This is the position scientists as such, and believers in the theory of naturalism, take up as to the possibility of the knowledge of truth to the human mind.

They are entirely consistent, therefore, when they arrive ultimately at the agnostic position, and contend that our knowledge must necessarily be confined to the world of experience, and that nothing can be known of the world beyond.

But they are fundamentally wrong in overestimating the place of the sense organs, and forgetting that while these have a part to play in life, they do not constitute the whole of life.
A far more satisfactory theory is that of _Rationalism_.

It is a theory that admits that the human mind has some capacity for working upon the data presented to it by the sense organs.