the R-values which play upon C and stimulate it to reactions, Avenarius calls f(R). The other he calls f(S).
And since the stability of C means that these two opposing factors are equal to each other and therefore nullify each other, Avenarius expresses the situation by the equation f(R)=-f(S), or f(R)+f(S)=0, which means that the result of the cooperation of f(R) and f(S) is that the system C does not depart from stability.
But if, starting with the system C in stability, we vary either f(R) or f(S), then it will no longer be true that f(R)+f(S)=0. To the degree to which one of the factors has been altered, the system C has departed from a state of stability. There has ensued a 'Vital Difference' and this vital difference is the difference between f(R) and f(S). One of the two factors is more effective in its influence than the other, and the difference between the two opposed forces is the vital difference. Since one of the factors is regarded as negative as related to the other, the difference is thus expressed: f(R) + f(S) > 0. The equation f(R) + f(S) =0 signifies that the vital difference has a value of zero, while the equation f(R)+f(S) >0 signifies that the vital difference is greater than zero.
The system C, however, tends always to return to stability, and the process of return must be a process of annulling the vital difference. There is thus a transition from stability through a condition of instability characterized by the existence of a vital difference back to stability, where the vital difference is reduced to zero. This series of states from stability to stability, Avenarius calls a vital series.
The vital series as thus described is a series of changes in the system C. The reason for assuming such series of changes is that parallel series of conscious states can be observed. The process of attention is an example. We start from what we may call a condition of indifference, or rest, or stability, then something awakens our interest and we begin to attend to some sort of a problem. We continue in a state of indecision and doubt and perplexity, looking forward, however, toward the solution which we hope to find. At last the solution comes, and we are at peace with ourselves again.
Now if to the changes of consciousness there is a parallel series of brain-events, they must form a series, and since each term of the series must be adequate to its effect in consciousness, the physiological series may be described with reference to its dependent mental states, and its terms considered as bearing relations to one another similar to the relations and proportions in the consciousness series. This is not so empty or so metaphysical as it may sound. We take it for granted, in a general way, that of the changes in brain tissue
