The term "grammatical category" refers to specific properties of a word that can cause that word and/or a related word to change in form for grammatical reasons (ensuring agreement between words).

For example, the word "boy" is a noun. Nouns have a grammatical category called "number ". The values of number are singular  (one) and plural  (two or more).

  1. The boy is playing.
  2. The boys are playing.

In sentence 1, "boy" is in its basic form, giving its "number" the value of singular. There is one boy and the related auxiliary verb "to be" is in the singular form (is).

In sentence 2, the form of "boy" has changed to "boys", giving its "number" the value of plural. There is more than one boy and the related "to be" is in the plural form (are).

In the above example, the "number" of "boy" influences the form of boy, and also influences the form of a related word (be). "Number" is a "grammatical category".

English has over twenty grammatical categories. Below we list the most common ones for English learners and summarise their main features.

Number

Number is a property of nouns and  pronouns, and indicates quantity. Number has two values:

  • singular : indicates one only
  • plural : indicates two or more
word typenumber
singularplural
nounboyboys
pronounIwe

Case

Case is a property of pronouns and  nouns, and expresses their relationship to the rest of the sentence. Case has three values (two of which do not apply to nouns):

  • subjective ¬†(pronouns only): when the word is the subject
  • objective ¬†(pronouns only): when the word is the object
  • possessive ¬†(pronouns and nouns): when the word indicates possession (ownership)
word typecase
subjectiveobjectivepossessive
pronounImemine
noun  boy's

Gender

Natural gender is a property of pronouns , and differentiates the sexes. Natural gender has three values:

  • masculine: indicates male
  • feminine: indicates female
  • neuter: indicates everything else
word typegender
masculinefeminineneuter
pronounhe/him/hisshe/her/hersit/its

Note that Old English had "grammatical gender" where words themselves had gender. Remnants of this are found in "natural gender", which is based on the sex of people rather than the gender of words.

Person

Person is a property of pronouns , and differentiates participants in a conversation. Person has three values:

  • first person: refers to the speaker
  • second person: refers to the hearer
  • third person: refers to all other people or things
word typeperson
1st2nd3rd
pronounI/me
we/us
youhe/him, she/her, it
they

Tense

Tense is a property of verbs, and most closely corresponds with location in time. Tense has two values:

  • past : indicates before now
  • present : indicates now (and sometimes before and after now)
word typetense
pastpresent
verbwas
did
had
worked
ran
am
do
have
work
run

Note that "future tense" is not shown here because strictly-speaking it is not a tense but a structure to talk about the future (after now).

Aspect

Aspect is a property of verbs, and expresses our view of the time structure of an activity or state. Aspect has three values:

  • simple : the time has no structure
  • continuous : expresses ongoing action
  • perfect : expresses completed action
word typeaspect
simplecontinuousperfect
verbthey workthey are workingthey have worked

Mood

Mood is a property of verbs, and relates to the speaker's feelings about the reality of what he is saying. Mood has three values:

  • indicative: expresses simple statement of fact
  • imperative: expresses command
  • subjunctive: expresses something desired or imagined
word typemood
indicativeimperativesubjunctive
verbJames stood up.Stand up!We insist that he stand.
Is it quiet enough?Be quiet!It is essential that you be quiet.

Voice

Voice is a property of transitive verbs*, and expresses the relationship of the subject to the action. Voice has two values:

  • active: the subject does the action
  • passive: the subject receives the action
word typevoice
activepassive
transitive verbThe cat ate the mouse.The mouse was eaten by the cat.

*A transitive verb can take a direct object. (An intransitive verb does not take a direct object.)

Degree

Degree is a property of gradable adjectives and  adverbs, and indicates amount. Degree has three values:

  • positive: indicates a basic quality
  • comparative: indicates a greater quality
  • superlative: indicates the maximum quality
word typedegree
positivecomparativesuperlative
gradable adjectivehappyhappierthe happiest
gradable adverbcarefullymore carefullythe most carefully

sources : Original Link