According to their meaning, morphological characteristics, and syntactical functions, words fall under certain classes called parts of speech.

We distinguish between notional and structural parts of speech.

Diagram

Notional Parts of Speech

The notional parts of speech perform certain functions in the sentence: the functions of subject, predicate, attribute, object, or adverbial modifier.

Structural Parts of Speech

The structural parts of speech either express relations between words or sentences or emphasize the meaning of words or sentences. They never perform any independent function in the sentence.

Notional PoSStructural PoS
Noun;
Adjective;
Pronoun;
Numeral;
Verb;
Adverb;
the words of the category of state;
the modal words;
Interjection.		Preposition;
Conjunction;
Particle;
Article.