arguments in favour of a certain important conclusion, though not quite in favour of the
conclusion that he thinks he is proving. He thinks he is proving that all reality is mental; what he
is proving is that we perceive qualities, not things, and that qualities are relative to the percipient.
I shall begin with an uncritical account of what seems to me important in the Dialogues; I shall
then embark upon criticism; and finally I shall state the problems concerned as they appear to me.
The characters in the Dialogues are two: Hylas, who stands for scientifically educated common
sense; and Philonous, who is Berkeley.
After a few amiable remarks, Hylas says that he has heard strange reports of the opinions of
Philonous, to the effect that he does not believe in material substance. "Can anything," he
exclaims, "be more fantastical, more repugnant to Common Sense, or a more manifest piece of
Scepticism, than to believe there is no such thing as matter?" Philonous replies that he does not
deny the reality of sensible things, i.e., of what is perceived immediately by the senses, but that we
do not see the causes of colours or hear the causes of sounds. Both agree that the senses make no
inferences. Philonous points out that by sight we perceive only light, colour, and figure; by
hearing, only sounds; and so on. Consequently, apart from sensible qualities there is nothing
sensible, and sensible things are nothing but sensible qualities or combinations of sensible
qualities.
Philonous now sets to work to prove that "the reality of sensible things consists in being
perceived," as against the opinion of Hylas, that "to exist is one thing, and to be perceived is
another." That sensedata are mental is a thesis which Philonous supports by a detailed
examination of the various senses. He begins with heat and cold. Great heat, he says, is a pain, and
pain must be in a mind. Therefore heat is mental; and a similar argument applies to cold. This is
reinforced by the famous argument about the lukewarm water. When one of your hands is hot and
the other cold, you put both into lukewarm water, which feels cold to one hand and hot to the
other; but the water cannot be at once hot and cold. This finishes Hylas, who acknowledges that
"heat and cold are only sensations existing in our minds." But he points out hopefully that other
sensible qualities remain.
Philonous next takes up tastes. He points out that a sweet taste is