times the contention that what appears to us as necessary connection among objects is really only
connection among the ideas of those objects: the mind is determined by custom, and "'tis this
impression, or determination, which affords me the idea of necessity." The repetition of instances,
which leads us to the belief that A causes B, gives nothing new in the object, but in the mind leads
to an association of ideas; thus "necessity is something that exists in the mind, not in objects."
Let us now ask ourselves what we are to think of Hume's doctrine. It has two parts, one objective,
the other subjective. The objective part says: When we judge that A causes B, what has in fact
happened, so far as A and B are concerned, is that they have been frequently observed to be
conjoined, i.e., A has been immediately, or very quickly, followed by B; we have no right to say
that A must be followed by B, or will be followed by B on future occasions. Nor have we any
ground for supposing that, however often A is followed by B, any relation beyond sequence is
involved. In fact, causation is definable in terms of sequence, and is not an independent notion.
The subjective part of the doctrine says: The frequently observed conjunction of A and B causes
the impression of A to cause the idea of B. But if we are to define "cause" as is suggested in the
objective part of the doctrine, we must reword the above. Substituting the definition of "cause,"
the above becomes:
"It has been frequently observed that the frequently observed conjunction of two objects A and B
has been frequently followed by occasions on which the impression of A was followed by the idea
of B."
This statement, we may admit, is true, but it has hardly the scope that Hume attributes to the
subjective part of his doctrine. He contends, over and over again, that the frequent conjunction of
A and B gives no reason for expecting them to be conjoined in the future, but is merely a cause of
this expectation. That is to say: Experience of frequent conjunction is frequently conjoined with a
habit of association. But, if the objective part of Hume's doctrine is accepted, the fact that, in the
past, associations have been frequently formed in such circumstances, is no reason for supposing
that they will continue, or that new ones will be formed in similar circumstances. The fact is that,
where psychology is concerned, Hume allows himself to