After we came out of the church, we stood talking for some time together of Bishop Berkeley's ingenious sophistry to prove the nonexistence of matter, and that every thing in the universe is merely ideal. I observed, that though we are satisfied his doctrine is not true, it is impossible to refute it. I never shall forget the alacrity with which Johnson answered, striking his foot with mighty force against a large stone, till he rebounded from it -- "I refute it thus."Also: Locke vs. Reid re: personal identity. "Reid's second criticism is his most famous and is often referred to as the case of the Brave Officer":
Suppose a brave officer to have been flogged when a boy at school, for robbing an orchard, to have taken a standard from the enemy in his first campaign, and to have been made a general in advanced life: Suppose also, which must be admitted to be possible, that when he took the standard, he was conscious of his having been flogged at school, and that when made a general he was conscious of his taking the standard, but had absolutely lost the consciousness of his flogging.
These things being supposed, it follows, from Mr LOCKE's doctrine, that he who was flogged at school is the same person who took the standard, and that he who took the standard is the same person who was made a general. When it follows, if there be any truth in logic, that the general is the same person with him who was flogged at school. But the general's consciousness does not reach so far back as his flogging, therefore, according to Mr LOCKE's doctrine, he is not the person who was flogged. Therefore the general is, and at the same time is not the same person as him who was flogged at school (Essays, 276).