rder. Then 'ideas' spring up in the order of
'sensations,' and this is the 'general law of association of
ideas.'[517] The synchronous sensations produce synchronous ideas and
the successive sensations successive ideas. Finally, the strength of
the association between the ideas depends upon 'the vividness of the
associated feelings, and the frequency of the association.'[518] Hume
had said that association depended upon three principles, 'contiguity
in time and place,' 'causation,' and 'resemblance.' Contiguity in time
corresponds to the successive, and contiguity in place to the
synchronous, order. Causation, as Brown had finally proved,[519] means
simply antecedence and consequence. 'Resemblance' remains and is, as
Mill afterwards says,[520] a most important principle; but in an
unlucky moment he is half inclined to reduce even 'resemblance' to
'contiguity.'[521] Resemblance is, he even suggests, merely 'a case of
frequency,' because we generally see like things together. When we see
one tree or sheep, we generally see several trees or sheep. J. S. Mill
mildly remarks upon this quaint suggestion as the 'least successful
simplification' in the book. He argues the point gravely. Sheep, it is
clear, are not seen to be like because they often compose a flock, but
are considered to be a flock because they are seen to be like. To do
James Mill justice, he drops the argument as soon as he has struck it
out. It is only worth notice as showing his aim. 'Likeness' seems to
imply a relation dependent on the ideas themselves; not purely
external and arbitrary. If we could get rid of likeness, all
association would ultimately be 'contiguity.' 'The fundamental law of
association,' as he says elsewhere,[522] 'is that when two things have
been frequently found together, we never perceive or think of the one
without thinking of the other.' The two ideas are associated as two
balls are associated when they are in the same box. So far as they are
themselves concerned, they might be separated without any alteration
in their own properties. What, then, corresponds to the 'box'?
Association depends upon relations of time and space. Things are
associated by occurring in succession or together; the red colour of a
rose is in the same place with the shape of the leaf; the scent is
perceived at the same time with the colour. The thunder follows the
lightning. What, then, he might ask, are 'time' and 'space'? Are they
'ideas' or 'sensations' or