The grammatical category

Grammatical category is a linguistic category which has the effect of modifying the forms of some class of words in a language.

Grammatical Categories
Grammatical Categories
Category of tense
Category of aspect
Category of mood
Category of voice

The grammatical category of tense
Tense is a grammatical category that locates a situation in time, that indicates when the situation takes place. In languages which have tense, it is usually indicated by a verb or modal verb, often combined with categories such as aspect, mood, and voice.
Typical tenses are present, past, and future.

The grammatical category of aspect
Aspect is a grammatical category that expresses how an action, event or state, denoted by a verb, relates to the flow of time.
A basic aspectual distinction is that between perfective and imperfective aspects (not to be confused with perfect and imperfect verb forms; the meanings of the latter terms are somewhat different).
Perfective aspect is used in referring to an event conceived as bounded and unitary, without reference to any flow of time during it ("I helped him").
Imperfective aspect is used for situations conceived as existing continuously or repetitively as time flows ("I was helping him"; "I used to help people"). Further distinctions can be made, for example, to distinguish states and ongoing actions (continuous and progressive aspects) from repetitive actions (habitual aspect).

The grammatical category of mood
In linguistics, grammatical mood is a grammatical feature of verbs, used to signal modality. That is, it is the use of verbal inflections that allow speakers to express their attitude toward what they are saying. Less commonly, the term is used more broadly to allow for the syntactic expression of modality — that is, the use of non-inflectional phrases.
Mood is distinct from grammatical tense or grammatical aspect, although the same word patterns are used to express more than one of these meanings at the same time in many languages, including English and most other modern Indo-European languages
Some examples of moods are indicative, interrogatory, imperative, emphatic, subjunctive, injunctive, potential.

The grammatical category of voice
In grammar, the voice (also called diathesis) of a verb describes the relationship between the action (or state) that the verb expresses and the participants identified by its arguments (subject, object, etc.). When the subject is the agent or does of the action, the verb is in the active voice. When the subject is the patient, target or undergoes of the action, the verb is said to be in the passive voice.

Word classes
The semantic criterion presupposes the evaluation of the generalized meaning, which is characteristic of all the subsets of words constituting a given part of speech. This meaning is understood as the “categorial meaning of the part of speech”. The formal criterion provides for the exposition of the specific inflexional and derivational (word-building) features of all the lexemic subsets of a part of speech. The functional criterion concerns the syntactic role of words in the sentence typical of a part of speech. The said three factors of categorical characterization of words are conventionally referred to as, respectively, “meaning”, “form”, and “function”.

The parts of speech problem
The parts of speech are classes of words, all the members of these classes having certain characteristics in common which distinguish them from the members of other classes. The problem of word classification into parts of speech still remains one of the most controversial problems in modern linguistics. The attitude of grammarians with regard to parts of speech and the basis of their classification varied a good deal at different times. Only in English grammarians have been vacillating between 3 and 13 parts of speech. There are four approaches to the problem:
Classical (logical-inflectional)
Functional
Distributional
Complex