Let the horizontal in Fig. 52 be the line of time, and let the three curves beginning at _a_, _b_, and _c_ respectively stand for the neural processes correlated with the thoughts of those three letters. Each process occupies a certain time during which its intensity waxes, culminates, and wanes. The process for _a_ has not yet died out, the process for _c_ has already begun, when that for _b_ is culminating. At the time-instant represented by the vertical line all three processes are _present_, in the intensities shown by the curve. Those before _c_'s apex _were_ more intense a moment ago; those after it _will be_ more intense a moment hence. If I recite _a_, _b_, _c_, then, at the moment of uttering _b_, neither _a_ nor _c_ is out of my consciousness altogether, but both, after their respective fashions, 'mix their dim lights' with the stronger _b_, because their processes are both awake in some degree. It is just like 'overtones' in music: they are not separately heard by the ear; they blend with the fundamental note, and suffuse it, and alter it; and even so do the waxing and waning brain-processes at every moment blend with and suffuse and alter the psychic effect of the processes which are at their culminating point. =The 'Topic' of the Thought.=--If we then consider the _cognitive function_ of different states of mind, we may feel assured that the difference between those that are mere 'acquaintance' and those that are 'knowledges-_about_' is reducible almost entirely to the absence or presence of psychic fringes or overtones. Knowledge _about_ a thing is knowledge of its relations. Acquaintance with it is limitation to the bare impression which it makes. Of most of its relations we are only aware in the penumbral nascent way of a 'fringe' of unarticulated affinities about it. And, before passing to the next topic in order, I must say a little of this sense of affinity, as itself one of the most interesting features of the subjective stream. =Thought may be equally rational in any sort of terms.= _In all our voluntary thinking there is some_ TOPIC or SUBJECT about which all the members of the thought revolve. Relation to this topic or interest is constantly felt in the fringe, and particularly the relation of harmony and discord, of furtherance or hindrance of the topic. Any thought the quality of whose fringe lets us feel ourselves 'all right,' may be considered a thought that furthers the topic. Provided we only feel its object to have a place in the scheme of relations in which the topic also lies, that is sufficient to make of it a relevant and appropriate portion of our train of ideas.