I’ve always thought of it as an “inference to the best explanation”.
Hmm. I think reading it this way could potentially raise other issues. If the proof is an inference to the best explanation, then it is not a demonstration, and some of its unintuitive consequences might be weighed against whatever plausibility hypothesis (2) has. (For what it’s worth, I don’t find it incredibly plausible.)
For example, there has been some discussion of Malebranche and occasionalism, but I see Berkeley as tending toward occasionalism in a weaker sense. For example, consider a case of change. On Berkeley’s view, our perceptions are changing because God is conveying different ideas to us. The instance of change appears to be a consequence of God’s “displaying” one perception after another. To try to get away from this understanding of the situation would require positing intrinsic principles of operation in certain sorts of perceptions. This sort of defeats the purpose of taking the idealist route to avoid positing matter. (It’s also the course that Berkeley does not take; he regards any sort of scientific generalizations as fortuitous and contingent, consequences of God’s benevolence to make the world intelligible and livable.)
Berkeley’s metaphysics also have undesirable implications for the problem of other minds that are compounded by trying to eliminate matter. (I would deny that one alternatively must “posit” matter as though it is a theoretical entity. I would deny that if we know “the external world” through perceptions, then
what we know are themselves perceptions.) Berkeley distinguishes categorically between perceivers (like you and I, and God) and things-perceived (ideas, perceptions). So I cannot perceive you. For that reason, it’s arguably difficult even to formulate the following scenario: You and I look at “the same” tree from “different angles.” (I use scare quotes to denote the ostensibly naive realist interpretation.) For Berkeley, is it really the same tree? Are our ideas the same? It seems as though they are not, because our perceptions are not the same. You see one side of the tree, and I see the other. So why should we be looking at the same tree? Unless there is something apart from our perception of the tree (ie. matter, something subsisting), there doesn’t seem to be any reason to tie our perceptions together as being of the same idea.
Relatedly, it’s plausible that two observers
can’t have the same idea, that part of the identity conditions of an idea is that the idea is the idea
of a particular observer. And that raises issues about whether God’s ultimate, grounding perceptions could be ours either. If you and I can’t have the same idea of a tree, then God and I can’t either, so that hypothesis (2) is not even an explanation.
Another problem is drawn from other natural-theological sources. Most philosophers who hold that God is simple would acknowledge the need to devise a simple analysis of his knowledge. God has a single intellective act, and his intellection is not compound. But many of those features will be incompatible with our own intellection and perception. So for our ideas to be God’s ideas, God’s ideas would have to be non-simple. (One could deny God’s simplicity. I regard that as pricey, but for someone who doesn’t, I think it is still problematic because Berkeley’s inference to the best explanation would be subject to a priori refutation if other demonstrations of God’s existence and nature succeed. And as Thomists like Haldane have argued, Aquinas’s proofs can be made to work even under idealist assumptions.)
The first explanation involves positing a new type of entity (matter) and involves tackling the problem of how things could come to exist or be destroyed. The second explanation doesn’t have any of those problems. It moves from the known to the known, instead of positing the entirely unknown (matter) to explain the known.
I don’t find the parsimony considerations too compelling because (as I said above), I think there are a lot of factors weighing against the explanatory adequacy of Berkeley’s idealism. (That said, my background in Berkeley is fairly limited, and I’m basing my critiques on the way he was presented in a course I took, which may not be representative of the views of people who take Berkeley seriously.)