At all events, they are willing to admit an ultimate substantial ground of thought and volition, provided it is not claimed that this substrate is of a spiritual nature. The _bare existence_ of some substrate, however, is all that we assert, for the present. Before leaving this topic, we wish to call attention to the fact that the subject of thought and desire is _active_ as well as _passive_. Mind, in other words, is not merely a persistent medium wherein passive mental states are maintained, but an active and synthetic principle as well. Mental processes, like those of judgment, reasoning, and recognition, require a unitary and unifying principle, which actively examines and compares our impressions and thoughts, in order to discern their relations to one another and to itself. Materialistic psychology, in spite of the plain testimony of consciousness, is all for ignoring the mind in its _active rôle_ as the percipient of the identities and discrepancies of thought, and for regarding mind as a mere complex of mental states or transient flux of fleeting imagery. It is well, then, to bear in mind the indubitable facts of internal experience, to which Cardinal Mercier calls attention. “English psychology,” he observes, “had attempted a kind of anatomy of consciousness. It made all consist in passive sensations or impressions. These impressions came together, fused, dissociated under the guidance of certain laws, principally those of similarity and dissimilarity. The whole process was entirely passive without the intervention of any active subject. It was psychology without a soul. Now that things are being examined a little more closely, psychologists find that there are a lot of conscious states that are without the slightest doubt active on the part of the subject. There are a number of mental states upon which the subject brings his _attention_ to bear, and attention (from _ad-tendere_) means activity. Ordinarily we do not know the intensity of a sensation without _comparing_ it with another preceding one. This work of comparison, or, as the English call it, discrimination, is necessarily _activity_. The Associationists had confounded the fact of coëxistence with the perception of similarity or dissimilarity. Supposing even that the coëxistence of two mental states were entirely passive, it still remains true that the notion of their similarity or dissimilarity requires an _act of perception_. It is absolutely impossible to conceive psychical life without an _active subject_ which _perceives_ itself as living, _notes_ the impressions it receives, _compares_ its acts, _associates_ and _dissociates_ them; in a word, there can be no psychology without a perceiving subject which psychologists call _esprit_, or with the English, ‘mind.’” (_Op. cit._, pp. 52-54—italics his.)