Consider the following parallel passages from Berkeley’s Principles and Dialogues:
so long as men thought that real things subsisted without the mind, and that their knowledge was only so far forth real as it was conformable to real things, it follows, they could not be certain that they had any real knowledge at all. For how can it be known that the things which are perceived, are conformable to those which are not perceived or exist without the mind? (PHK sect. 86)
It is your opinion, the ideas we perceive by our senses are not real things but images or copies of them. Our knowledge therefore is no farther real, than as our ideas are the true representations of those originals. But as these originals are in themselves unknown, it is impossible to know how far our ideas resemble them, or whether they resemble them at all. We cannot therefore be sure we have any real knowledge. (DHP, L&J p. 246)
It is usually thought that in these two passages Berkeley is assuming some sort of internalism about justification. That is, he is assuming that we can’t gain knowledge by means of the senses unless we know that the senses are reliable. On this reading, Berkeley is arguing that representative realism leads to general skepticism, because of the impossibility of a non-circular justification of trust in the senses. Reid probably read Berkeley this way, and this was probably the reason why Reid thought that externalism about justification would allow him to escape Berkeley’s argument.
Now, I don’t want to deny that internalist assumptions may be in the background at many points in Berkeley’s writings, but I do want to point out that, as the bolded phrases show, these texts make no such assumption. The structure of the argument in these two passages is rather the following:
- If representative realism is true, then we gain knowledge by means of the senses only if our perceptions match mind-independent objects.
- We cannot know that our perceptions match mind-independent objects.
- If representative realism is true, we cannot know that we gain knowledge by means of the senses.
In other words, representative realism engenders second-order skepticism; it prevents us from knowing that we know. Externalism is not a way of escaping from this argument. Unless the externalist-representative-realist wants to allow knowledge of the reliability of the senses to rely directly or indirectly on the senses themselves (see Van Cleve), it would seem that she is stuck accepting the second-order skeptical thesis. Berkeley, however, finds the second-order skeptical thesis unacceptable.
It is in fact not surprising that much of Berkeley’s discussion should take place at the second-order. After all, the structure of the dialectic, both between Berkeley and his real-world opponents and between his fictitious characters Hylas and Philonous, is a debate about whether ‘the vulgar’ or ‘the mob’ or ‘the illiterate bulk’ have knowledge of familiar objects like apples, tables, and cherry trees, and if so how. Berkeley’s complaint against his opponents is that, on their theories, it cannot be proved that the gardener knows his cherry tree. He claims that his own theory does not have this defect: the philosopher who has grasped Berkeley’s arguments thereby comes to know that the gardener knows that his cherry tree exists.
(Cross-posted at blog.kennypearce.net.)