…I use the word “tendency” to denote, in the concrete a real would-be, and in the abstract the reality of a would-be, which is not the cause but is the reality of a disposition in a kind of event, whether produced by a cause or merely by the absence of any determining cause, in consequence of which[,] or more accurately speaking by the meaning of which expression[,] that kind of event, if the tendency were known[,] could be predicted to happen, either invariably, or usually, or often, or sometimes, as the case might be, in the long run.