1. So to apprehend in all particular instances the relation of cause and effect, as to connect the two extremes in thought according to the order in which they are connected in nature (for the modus operandi is, and must ever be, unknown to us), is the final object of science. This treatise has shown, that there is special reference to such an object in the constitution of the intellectual faculties. There is a sphere of thought which comprehends things only as coexistent parts of a universe; but there is also a sphere of thought (Chap, xi.) in which they are apprehended as links of an unbroken, and, to human appearance, an endless chain—as having their place in an order connecting them both with that which has gone before, and with that which shall follow after. In the contemplation of such a series, it is impossible not to feel the pre-eminence which is due, above all other relations, to the relation of cause and effect.

Here I propose to consider, in their abstract form, some problems in which the above relation is involved. There exists among such problems, as might be anticipated from the nature of the relation with which they are concerned, a wide diversity. From the probabilities of causes assigned à priori, or given by experience, and their respective probabilities of association with an effect contemplated, it may be required to determine the probability of that effect; and this either, 1st, absolutely, or 2ndly, under given conditions.