carrying out this thought, the author used to say: "In fact future nature is not given to us, just as the past is not given to us. Sense-data and thought unite at every instant afresh to form a new judgment and a new postulate. Only in the present has any judgment evident validity. And our postulate of causal relation is just a way of looking at this world of conceived past and future data. Such postulates avoid being absurd efforts to regulate independent facts of sense, because, and only because, we have in experience no complete series of facts of sense at all, only from moment to moment single facts, about which we make single judgments. All the rest we must postulate or else do without them." Thus one reaches a skepticism as nearly complete as is possible to any one with earnest activity of thought in him. From moment to moment one can be sure of each moment. All else is postulate.
From the depths of this imperfectly defined skepticism, which seemed to him provisionally the only view he could adopt, the author escaped only by asking the one question more: "If everything beyond the present is doubtful, then how can even that doubt be possible?" With this question that bare relativity of the present moment is given up. What are the conditions that make doubt logically intelligible? These conditions really transcend the present moment. Plainly doubt implies that the statement doubted may be false. So here we have at least one supposed general truth, namely, "All but the immediate content of the present moment’s judgment, being doubtful, we may be in error about it." But
