It's not obvious what's obvious

"It ain't obvious what's obvious". Thanks to the Maverick for that insight by Hilary Putnam.  I suppose everyone knows the mathematician's joke about the lecturer how - discussing some result - says 'That's obvious'.  He then pauses, looks down, then goes off for about twenty minutes.  Then he comes back and announces 'Yes, it's obvious'.

Judging from the comments, there's been a bit of misunderstanding about my position on the 'thin conception' of existence.  I don't necessarily agree with the conception.  My question is whether the brief arguments given by Maverick, and which seem as obvious as day to him, really are obvious. Now I think, pace Dr. Putnam, there is a simple test for obviousness. If you can state your position or argument in less than about five sentences, and if the terms are clear or well-defined, or have a common and undisputed meaning, if any assumptions underlying the position are beyond dispute, and if all deductive steps are valid, then  it is obvious. Otherwise it isn't.

Now Maverick's argument, as I understand it, is this:

The thin conception of 'exists' is that 'An F exists' means the same as 'The concept *F* is instantiated'
But if *F* is instantiated, then it is instantiated by an individual that exists
Therefore the thin conception of 'exists' is circular

This is deceptively simple, but fails my test for obviousness.  Why?  The subject of the conclusion is 'the thin conception of exists'.  The predicate is 'circular'.  The predicate of the conclusion is called the 'major term' and it is an undisputed rule of logic that the major term should appear in the premisses. Which of course it doesn't.  This would probably be fine if the idea of a circularity were undisputed and clear, by I have argued elsewhere that it isn't. It is very slippery.

So what is needed is an argument of the following form:

The thin conception of existence is of form X
Any conception of form X is circular
The thin conception of existence is circular.

I would accept any argument of that form as 'obvious'.  And I hope that clears me of any charges of being disingenuous.