Sure, as long as 4 doesn’t lead a person to equivocation.
Consider my argument about God being the conjunction of cows and crows. Whatever else you may think of it, you have to acknowledge that it's not going to convert anybody to theism, and the reason why is because the definition of "God" in the first premise isn't actually addressing theism. And that's been my contention throughout this thread, is that when you make an existential argument about a concrete object, all such premises fail to accurately pinpoint the object to be argued for (or against), even honest attempts. Again, classic rebuttal to the Cosmological argument is that showing that there is a first cause is wholly insufficient to conclude that there is a God in any meaningful use of the term. i.e, a person can agree that the Cosmological argument is sound and remain an atheist. I'm saying all arguments of that type (deductive, existential about a concrete) have that same problem to a greater or lesser degree. That's what I'm arguing here.
That’s doesn’t read to me as just a declaration of definition. That’s also an assertion that there is a larger object in your right hand at this moment, which makes arguing that there is such an object (that it exists) circular. If you don’t intend that part of the premise, then it reads odd to me, but we can say “Brick A is defined as 'the largest object in my hand right at this moment”, which no implicaton intended as to whether or not there is such an object.
Sure, without the assertion that the object exists, that the object is named Brick A for the purpose of the argument is true.
You haven’t established it in any way, and since you aren’t the ‘you’ spoken of in the premise, you have no way TO establish it in anyway, so whomever you’re addressing is free to say ‘no I don’t’ and then you’re screwed. But even if they concede it, what you have is two premises here:
2a) You see and feel something
2b) The thing that you see and feel is the larger object in my hand.
2a is fine other than the problem I cited above, 2b makes your argument circular, as it asserts the existence of the thing you are trying to prove the existence of. Now if you want to modify it to read something like “You see and feel what appears to be the larger object in my hand”, then that problem goes away, but it underlines the problem with premise 3.
And that premise is simply false, or circular, or both. If you really mean to carry over your assertion taht there is in fact an object from premise 2, then you’re asserting what you intend to prove, which is circular. If you don’t mean to carry over such an assertion, then what you really have is the premise that ‘you could not see and feel what appears to be an object in my hand unless the object existed’, which is clearly false as we have any number of counter examples- even if you want to say that people having hallucinations are seeing figments of their imagination and those figments are real, that figment certainly doesn’t meet the criteria in premise 1 anymore- it’s not in your hand, it’s in their mind (if indeed it can be said to be anywhere).
So in summary, the most cheritable way I can read your argument (not trying to twist it, trying to avoid as many of the problems with it as written as I see, is)
1.) “Brick A” is defined as 'the larger object in my hand".
2.) You see and feel what appears to be an object meeting the criteria for “Brick A”
3.) You could not have such sensations if the object did not exist.
In which case there’s no circularity or reliance on existence as a predicate, but 3 is false if ‘the object’ means an object meeting the criteria for “Brick A” defined in 1. It is generally the case that when we see and feel objects they exist, and when we see and feel things we rightly infer that they exist, but exceptions exist as well- people do sometimes see and feel what appears to be an object in a hand where in there is actually no object in the hand.
Now, if you want to define a ‘hand’ in premise one in such a way that the mere appearence of a hand sastisfies the criteria, you might be able to get around this problem, but I wonder how you feel about that.