hink, ever have exactly
similar sensations related to the same physical object at the same
moment; on the other hand, even the most private sensation has
correlations which would theoretically enable another observer to infer
it.

That no sensation is ever completely public, results from differences of
point of view. Two people looking at the same table do not get the same
sensation, because of perspective and the way the light falls. They get
only correlated sensations. Two people listening to the same sound do
not hear exactly the same thing, because one is nearer to the source of
the sound than the other, one has better hearing than the other, and
so on. Thus publicity in sensations consists, not in having PRECISELY
similar sensations, but in having more or less similar sensations
correlated according to ascertainable laws. The sensations which strike
us as public are those where the correlated sensations are very similar
and the correlations are very easy to discover. But even the most
private sensations have correlations with things that others can
observe. The dentist does not observe your ache, but he can see the
cavity which causes it, and could guess that you are suffering even
if you did not tell him. This fact, however, cannot be used, as Watson
would apparently wish, to extrude from science observations which are
private to one observer, since it is by means of many such observations
that correlations are established, e.g. between toothaches and cavities.
Privacy, therefore does not by itself make a datum unamenable to
scientific treatment. On this point, the argument against introspection
must be rejected.

(2) DOES EVERYTHING OBSERVABLE OBEY THE LAWS OF PHYSICS? We come now to
the second ground of objection to introspection, namely, that its data
do not obey the laws of physics. This, though less emphasized, is,
I think, an objection which is really more strongly felt than the
objection of privacy. And we obtain a definition of introspection more
in harmony with usage if we define it as observation of data not subject
to physical laws than if we define it by means of privacy. No one would
regard a man as introspective because he was conscious of having a
stomach ache. Opponents of introspection do not mean to deny the obvious
fact that we can observe bodily sensations which others cannot observe.
For example, Knight Dunlap contends that images are really muscular
contractions,* and evidently regards our