O substantive it is a grammatical class, therefore it is an object of study in morphology. However, within the sentence, it has a syntactic function. Therefore, it is important to understand it from these two prisms, that is, morphological and syntactic.
Every grammatical class is divided between variable and invariant words, the substantive it composes the variables, those that can be inflected. One might ask: what is flexing? It's change, vary. In the case of nouns, this variation will be in relation to gender (female and masculine), number (singular and plural) and degree (augmentative and diminutive).
It is essential to understand this, because if we leave morphology and move to syntax, more precisely to Nominal Concordance, it is essential that apply this information, because then it will be easy to understand why the article, the numeral, the adjective and the adjective pronoun must agree with the substantive. If it is variable, then the terms that relate to it must agree, that is, they must match.
You nouns can be:
Primitives
When they are not formed from another word. Example: Book
Derivatives
Formed from another word. Example: Bookstore
Simple
Names that have only one word. Example: rain
Compounds
Names consisting of two words. Example: Umbrella
Concrete
When your existence is independent, that is, you don't need something or someone to manifest. Example: Table
Abstracts
When your existence depends on something or someone. Example: Anger
Collectives
When they indicate a collection, a set of beings, as long as they belong to the same species. Example: Fauna (animals of a region)
Ordinary
When they don't specify, on the contrary, they generalize. Example: boy.
Own
When they specify, when they particularize. Example: John.
There are many classifications, but what defines a word as substantive? Your ability to name. Think of a word. Analysis. What is it for? To name? So it's noun. Chair, table, bag, blackboard, diary, book, computer, calendar, love, in short, you name it, it's a noun.
By Mayra Pavan
Graduated in Letters
Source: Brazil School - https://brasilescola.uol.com.br/o-que-e/portugues/o-que-e-substantivo.htm