"The word 'dog' has meaning" but I can't say "That dog has meaning".
What is the difference between the word 'dog', and the phrase 'that dog'?
Why does one have meaning, while the other doesn't? One exists in the mind, while the other exists in the mind and in reality. The only difference is that the referent of the latter also happens to exist outside of our mind. But I would argue that the referent in the phrase 'that dog', is in fact not outside of our minds, otherwise it could not be known, for to be known, is to be in the mind. Therefore, there is no essential difference between the word 'dog', and the phrase 'that dog'.
I cannot understand "self-contradictory idea (concept)". Since we cannot think of anything which a contradictory sentence could refer to, how could we justify saying that we are having any idea or concept at all?
The definition of a being, is equivalent to all propositions which describe it.
Two descriptive propositions which refer to the round-square, are:
Entity p is round
Entity p is square
Given that to understand the descriptive propositions which refer to to an entity, is to understand what the entity is, and descriptive propositions can contradict, then we can understand an entity which is incoherent. Do you mean by 'having an idea of', to have a visual representation of?
I think I am correct to assume that you and he use "things with being" synonymously with "existent things". Correct me if I'm wrong.
Technically, I would use the word 'existence' in the same or similar way to Aristotle. Essence, is being, and Existence is non-being. (Ex-istence is coming from essence to essence). Dealing what the classic problem with the 'one-and-the-many'. The pre-socratics argued mainly with 2 seemingly contradictory views -- that everything is one and nothing changes, and that everything is many and everything is always changing. In this case, I am using it in the vulgar sense to mean 'a thing which is'. So for an entity to be itself, it must have have essence, and to have essence, is to be 'a thing which is'. Untimately, the word existence is just as meaningful as the word 'is' is. For example, what do we mean when we say, 'a cat exists'? Do we mean that a cat is physical, round, red, short or cogent? Do we mean that we can interact with it and make observations about it? This is why I claim that to say a being does not exist, is to commit a self-contradiction, because we end up saying, a 'being is not a being', or 'an entity which is, isn't'.
For example. What is a Pegasus? It is a horse with wings, and can fly.
Can non-existing entities fly? Of course not, since non-being, can not do anything.
Does Pegasus exist?
To say that the word 'pegasus' is meaningless, is to deny the meaningfulness of possible-world semantics, and all counterfactual statements. For there is a possible-world in which pegasus does fly.