Whenever you have an idea of a thing, you define that thing. You define what that thing looks like, its properties, its parts, its environment etc. — litewave

You could say you "define" it as your idea, sure. No one is defining a unicorn as "not being what it is" though.

The thought of a unicorn is not a unicorn, and doesn't mean a unicorn is consistent. The thought produces a memory of an artificial human experience of a unicorn. That's about as good as I can word it. The memory is distinguishable from the memory of an actual experience of a unicorn most times, but not always. The existence of that memory or the having of that imagined experience does not instantiate a unicorn. I cannot even imagine my own wife. I can only imagine my experience of my wife.
Now if logical consistency is equated with ontic existence, then the unicorn exists. Does 'instantiation' also mean that same thing? It has to. Let's say a magic amulet (that changes color in the presence of danger, kind of like Bilbo's sting) is logically consistent, but it happens to be instantiated in a place with no observers. What does that mean? Danger to what? Well, perhaps the nearby rock formation, in danger of the impending frost breaking it up. But the amulet is identical to itself, and is not what it isn't.

Anyway, that's my attempt to describe something improbable but not logically inconsistent, and with an instantiation not dependent on idealistic ontology. This sort of thing is implied by equating existence to consistency. I cannot find fault with the assertion, but it seems to weaken the whole concept of ontology if there is no distinction with possible but nevertheless nonexistent, an intuitive state that I assign things like my older sister.

Final comment on what Chany wrote:

You would have to embrace multiverse theory and say that every single possible world is a real world, as real and concrete as the actual world. This leads to a contradiction, as it is also logically coherent (possible) that only the actual world exists and that the other possible worlds do not exist — Chany

I don't think this is a contradiction. There can be a logically consistent MW universe as well as a single world one, and both of them contain this same state as we see here. The truth of the other one seems not to contradict how ours works, and MW being false here does not preclude the existence of those alternate worlds. Ouch. Did I just contradict myself? This uni-world is identical to one world of the MW setup. They would seem to be the same thing, so MW has to be true given the definitions posited here.

Now what made me change my mind?
You said "It is logically consistent that some logically consistent thing (other worlds for instance) to not exist". Not sure if you can use that as an argument against, since it boils down to "It is logically consistent that some logically consistent thing is not logically consistent". That is not logically consistent, so the nonexistence of the other world is false. If you can make a paradox of it, then we have something.

No one is defining a unicorn as "not being what it is" though. — Terrapin Station

If someone imagines a unicorn existing on our planet, then they define it inconsistently, even when they are not aware of the inconsistency. They define it as existing in a place where it doesn't exist, and thus as something that is what it is not.

Now if logical consistency is equated with ontic existence, then the unicorn exists. Does 'instantiation' also mean that same thing? — noAxioms

I am not sure what you mean by "instantiation". I mean the instatiation to be the relation between an abstract (general) thing (property) and its instance, for example between red color and a particular red thing. Both the red color and the particular red thing exist.

If Joe believes that there's an extramental/objective unicorn on Main Street, then we could say that he "defines" as his idea that there's an extramental/objective unicorn on Main Street. It's important to note that he's only defining his idea--and that's all one can do. We can't say that Joe's idea is thus that no extramental/objective unicorn exists on Main Street--that would be exactly the opposite of his idea that he defined.

If Joe believes that there's an extramental/objective unicorn on Main Street, then we could say that he "defines" as his idea that there's an extramental/objective unicorn on Main Street. — Terrapin Station

But his idea is inconsistent, because it is about an inconsistent thing (a unicorn on Main Street).

But his idea is inconsistent, because it is about an inconsistent thing (a unicorn on Main Street). — litewave

How would you state a specific example of P & ~P re the idea?

How would you state a specific example of P & ~P re the idea? — Terrapin Station

Joe has the idea "There is a unicorn on Main Street". He may not know that there is no unicorn on Main Street, but his not knowing it doesn't make his idea consistent. He may only be aware of "There is a unicorn on Main Street" but his idea is de facto "There is a unicorn on Main Street & there is no unicorn on Main Street" (because there is in fact no unicorn on Main Street).

He might as well have the idea that a circle is a square without knowing that a circle is not a square, but his not knowing it doesn't make his idea consistent. He may only be aware of "A circle is a square" but his idea is de facto "A circle is a square & a circle is not a square" (because a circle is in fact not a square).

Joe has the idea "There is a unicorn on Main Street". He may not know that there is no unicorn on Main Street, but his not knowing it doesn't make his idea consistent. He may only be aware of "There is a unicorn on Main Street" but his idea is de facto "There is a unicorn on Main Street & there is no unicorn on Main Street" (because there is in fact no unicorn on Main Street). — litewave

Joe's idea is NOT that there is not a unicorn on Main Street. So his idea isn't inconsistent in that respect.

You can't say that someone's belief that P is inconsistent with the fact that not-P. Logical contradictions have to be cases of asserting and denying the same proposition, in the same respect, etc., otherwise you're committing the fallacy of equivocation.. This wouldn't be in the same respect. One is a person's belief, and the other is a fact (filtered through some other person's belief).

So you would say that Joe's idea that a circle is a square is consistent?

You're not getting the square circle thing right, first off. The issue there isn't the shapes. It's the idea of constructing a square equal in area to a given circle.

Anyway, note that I'm not claiming that someone can not have an inconsistent belief. So jumping to other examples isn't very useful.

You're not getting the square circle thing right, first off. The issue there isn't the shapes. It's the idea of constructing a square equal in area to a given circle. — Terrapin Station

I said nothing about the area of a circle or a square. I said a circle is a square, which is a clearly inconsistent statement. The statement "There is a unicorn on Main Street" is inconsistent too, even though it may not be obvious.

Anyway, note that I'm not claiming that someone can not have an inconsistent belief. So jumping to other examples isn't very useful. — Terrapin Station

The example about the circle is similar to the example about the unicorn, only in the unicorn example the inconsistency may not be obvious. So I wanted to show the parallels. Joe's idea is inconsistent no matter whether he believes it. If he believes it then his belief is inconsistent too.

Okay, so sticking with the unicorn example, what's the proposition that's both being asserted and denied unequivocally? He's not denying "There is a unicorn on Main Street." So what proposition is both he asserting and denying?

When I explained all of this earlier:

Joe's idea is NOT that there is not a unicorn on Main Street. So his idea isn't inconsistent in that respect.

You can't say that someone's belief that P is inconsistent with the fact that not-P. Logical contradictions have to be cases of asserting and denying the same proposition, in the same respect, etc., otherwise you're committing the fallacy of equivocation.. This wouldn't be in the same respect. One is a person's belief, and the other is a fact (filtered through some other person's belief).

You didn't address any of it head on, which I should have made a point of then. You deflected rather. So it's time to address it head on.

Okay, so sticking with the unicorn example, what's the proposition that's both being asserted and denied unequivocally? He's not denying "There is a unicorn on Main Street." So what proposition is both he asserting and denying? — Terrapin Station

It is contained in the definition of a unicorn that it doesn't exist on Main Street (at least in our world), just as it is contained in the definition of a circle that it is not a square. So the idea that a unicorn exists on Main Street says that something that doesn't exist on Main Street exists on Main Street.

It is contained in the definition of a unicorn that it doesn't exist on Main Street (at least in our world), just as it is contained in the definition of a circle that it is not a square. So the idea that a unicorn exists on Main Street says that something that doesn't exist on Main Street exists on Main Street. — litewave

Joe's not saying anything about a unicorn not existing on Main Street, is he? So where is a proposition that a unicorn doesn't exist on Main Street coming from?

Joe's not saying anything about a unicorn not existing on Main Street, is he? So where is a proposition that a unicorn doesn't exist on Main Street coming from? — Terrapin Station

It is coming from the same source as the proposition that a circle is not a square: from reality. Every thing exists in the sense in which it is defined (constituted, placed) in reality. Unicorns don't exist on Main Street; it's part of their definition.

It is coming from the same source as the proposition that a circle is not a square: from reality. — litewave

I don't agree that "reality itself" issues propositions. It's something that individual persons do.

I don't agree that "reality itself" issues propositions. It's something that individual persons do. — Terrapin Station

Propositions are a kind of properties of reality. People's statements refer to these properties.

Propositions are a kind of properties of reality. — litewave

No. Propositions are the (meanings of) the statements.

No. Propositions are the (meanings of) the statements. — Terrapin Station

Propositions are the meanings of statements, that is, the referents of statements in reality.

Take the proposition "There is no unicorn on Main Street". The proposition is true in our world, so it is a property (characteristic, feature) of our world. On the other hand, the proposition "There is a unicorn on Main Street" is false in our world, so it is not a property of our world. Maybe it is a property of some other world.

The proposition "A circle is not a square" is a tautology because it is true in every possible world, so it is a property of every possible world. On the other hand, its negation is false in every possible world, so it is not a property of any world.

Propositions are the meanings of statements, that is, the referents of statements in reality. — litewave

Meanings are specific mental events in particular individual's brains.

And truth value is a subjective judgment particular individuals make about the relations of propositions to other things.

Do you think there is no objective truth? No external reality?

External reality, yes. Objective truth, no.

But a statement is true if it corresponds to reality. It is irrelevant whether anyone subjectively judges it as true.

What it is for a statement to correspond to reality is for a person to make a judgment about the relation of the statement--and specifically its meaning, which is a subjective phenomenon, to reality.

Also, correspondence is just one possible truth relation. Different people use different relations.

The idea of a statement corresponding to reality mind-independently is simply nonsensical. Mind-independently, "statements" are simply sets of marks on paper, marks on a screen, or soundwaves propagating through a medium like air, etc.

It's fine to say "P is true if P corresponds with reality," but then we need to ask, "Okay, how, exactly, does that obtain? How, exactly, does a statement correspond with reality? How does it work 'mechanically'?" And the answer to that is that a person makes a judgment about it.

It's fine to say "P is true if P corresponds with reality," but then we need to ask, "Okay, how, exactly, does that obtain? How, exactly, does a statement correspond with reality." And the answer to that is that a person makes a judgment about it. — Terrapin Station

Words have their referents in reality. Once it is chosen which words refer to what in reality, it is an objective fact whether a statement made of those words corresponds to reality (accurately describes reality), not a matter of subjective judgment. If you jump out of window you will fall, no matter what anyone's judgment may be.

Once it is chosen which words refer to what in reality, it is an objective fact whether a statement made of those words corresponds to reality — litewave

Could you describe how you believe that works?--That is, describe the mechanics of it in some detail?

Could you describe how you believe that works?--That is, describe the mechanics of it in some detail? — Terrapin Station

"If you jump out of window you will fall."

It is well known what the words in this statement refer to. Do you think that the truth of this statement depends on someone's judgment? That the statement may not be true and so you will not fall if you jump out of window? (of course we assume that usual conditions hold, such as the presence of gravity, the position of the window above the ground, you not having wings etc., which I am not going to enumerate)

"If you jump out of window you will fall." — litewave

What I'm asking you is how it works--basically in "mechanical" terms--that those words refer to something. You're claiming that they refer to something mind-indepedently. Well, how does that work exactly?

We can start wherever you like. With those marks on the screen, or we can imagine someone making those sounds or whatever. So, there are those marks on the screen, and mind-independently, they refer by . . . ? (And then you fill in the blank explaining the process by which this works.)

What I'm asking you is how it works--basically in "mechanical" terms--that those words refer to something. You're claiming that they refer to something mind-indepedently. Well, how does that work exactly? — Terrapin Station

Words are just our names for things and relations in reality. For example, people in English speaking countries agreed to use the word "window" as a name for the openings in the walls of houses that serve to let in light and air. Words are useful in communication. If you want to tell someone about a window you just utter a simple sound instead of having to draw a window or show them a physical one.

The choice and use of a word is mind-dependent but the thing in reality that the word refers to is generally not. Whether there is a thing called "window" in a particular wall of a house is true or untrue regardless of how we call it and even regardless of whether anyone makes a statement about it. The truth is completely mind-independent. The proposition "There is a window in the wall" is a special kind of complex property, with a subject-predicate structure, and when such a property is instantiated in a world, it is true in that world.

And if someone makes the statement "There is a window in the wall" then of course it requires a mind to make a statement but whether the statement is true depends on whether there is a window in the wall in reality, not on someone's judgment.