Definitions

A noun is the name of an object.

For example

The words house, tree, Boston, and goodness in their normal use are nouns.

The word object, as here used, should be carefully distinguished from the same term employed in the Syntax section to denote the complement of the transitive verb. Here, it denotes every species of existence, material or immaterial, which may be considered independently or alone; and is opposed to the term attribute, which always represents something dependent upon, belonging to, or inherent in, an object.  An attribute, when regarded as an object to the mind, that is, when abstracted from that to which it belongs, becomes an object of itself.

The name of such an attribute is a noun, and is usually derived from the word denoting the attribute.

For example

The word goodness derived from the adjective good is a noun.
The word brightness derived from the adjective bright is a noun.

When a word, a syllable, a letter, or a symbol of any kind is spoken of as an object, it is a noun.

For example

In the sentence:
We is a personal pronoun.
the word We is being used as a noun.
In the sentence:
Un is a prefix.
the syllable Un is being used as a noun.
In the sentences:
‘A’ is a vowel. ‘+’ is the sign of addition. ‘,’ is a comma.
the letter ‘A’ and the symbols ‘+’ and ‘,’ are used as nouns.

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