A radical form of empiricism arising from the ontological view that the nature of things is not external or independent of the perceiver, but entirely dependent upon the related qualia experienced by the perceiver of the thing(s).
Philosopher A.J. Ayer included phenomenalism in his Logical Positivism, postulating that if a proposition is to be considered true, some sensory experience can verify it as being true. This is the verification principle. Thus for phenomenalists, all statements about the world are statements about sensory experience of the world, whether actual or possible (as in a proposition, for analytical purposes).
Perhaps the most significant criticism of phenomenalism is the argument that the verification principle is itself incapable of being empirically verified. This would place propositions about the physical world in the same position as any ethical or aesthetic proposition, which cannot be judged true or false because they cannot be verified.
Web Resources On Phenomenalism
Knowledge - Phenomenalism
Phenomenalism in Wikipedia
Phenomenalism in the Catholic Encyclopedia
Book Resources On Phenomenalism
The Logic of Scientific Discovery by Karl Popper
The Self-Aware Universe by Amit Goswami
The Will to Power by Friedrich Nietzsche