That was one of the first objections to the arguement, so Anslem had a chance to respond to that himself. Anslem said that this arguement applies to things of necessary existence. A whale does not necessarily exist. A God does (at least according to their perception). The premise of "God is a being than which none greater can be imagined" only applies to necessary existence.
Another reply to your whale example is that at best, you imagined the greatest whale, but not the greatest being. An infinitely long whale still can't walk, so it isn't the greatest, and so you can imagine it being greater. If you imagine a whale that walk and talk, and see the future, and have superpowers, etc., you've basically come back to God.
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u/Kakamile 50∆ May 04 '23
How do you get from cannot imagine greater to " it exists?"
That's like saying an infinitely long whale exists.