Here's why:
* Parts of speech describe the grammatical function of words in a sentence. Examples include nouns, verbs, adjectives, adverbs, pronouns, prepositions, conjunctions, interjections.
* Contractions are simply shortened forms of words or phrases, created by combining two words and replacing some letters with an apostrophe.
For example:
* "I am" becomes "I'm"
* "You are" becomes "You're"
* "Cannot" becomes "Can't"
While contractions are helpful for creating informal and conversational writing, they don't change the grammatical function of the words they replace. The parts of speech remain the same:
* "I'm" still acts as a pronoun (I) followed by a verb (am).
* "You're" still acts as a pronoun (you) followed by a verb (are).
* "Can't" still acts as a modal verb (can) followed by a negation (not).
Therefore, contractions are considered stylistic choices rather than distinct parts of speech.