§ 6. Accordingly the whole notion of a substantial unity in things behind the multiplicity of their states or qualities has been regarded with disfavour by many students of positive science. The qualities being all that interests us in things, and the notion of an indeterminate substratum contradictory, we ought, it is argued, to identify the thing and the series of its states and qualities without more ado. From this point of view the thing ceases to be an unknown somewhat, which in some mysterious way _has_ properties; it becomes the properties themselves thought of as a collection. It is no longer the unperceived _this_ which _has_ warmth, redness, etc., it is the warmth, the redness, and the rest of the sensible qualities taken collectively. For phenomenalist Metaphysics, as for associationist Psychology, the thing is a “bundle of attributes” and nothing more. When we ask how, if a “thing” is merely the series or sum of its attributes, and possesses no underlying unity to which the attributes belong, the whole of our ordinary language about things comes to be constructed on the contrary assumption, how it is that we always talk and think as if every “bundle” of attributes were owned by something of which we can say that it _has_ the quality, we are met by the phenomenalist with a reference to Psychology. Owing to the fact, which Phenomenalism and Associationism are content to accept as ultimate, that sensible qualities are always presented to our perception in definite groups, it is argued that the thought of any one member of such a group is enough to revive by association the thought of the other qualities which have regularly been presented simultaneously with itself or in immediate succession to it. Hence, because thus associated in our perception, the group comes naturally, though illegitimately, by one of those mental fictions of which Hume treats so fully, to be thought of as one, though it is actually a discrete multiplicity. The unity of the thing thus lies not in itself, but solely in our way of perceiving and thinking.