Page "Existence" Paragraph 22

In mathematical logic, there are two quantifiers, " some " and " all ", though as Brentano ( 1838 – 1917 ) pointed out, we can make do with just one quantifier and negation.

The first of these quantifiers, " some ".

is also expressed as " there exists ".

Thus, in the sentence " There exists a man ", the term " man " is asserted to be part of existence.

But we can also assert, " There exists a triangle.

" Is a " triangle " — an abstract idea — part of existence in the same way that a " man " — a physical body — is part of existence?

Do abstractions such as goodness, blindness, and virtue exist in the same sense that chairs, tables, and houses exist?

What categories, or kinds of thing, can be the subject or the predicate of a proposition?