Nouns and pronouns can both change form, but the reasons and how they change are different:
Nouns:
* Number: Nouns change form to show whether they are singular (one) or plural (more than one).
* Example: cat (singular) vs. cats (plural)
* Case: Nouns sometimes change form to show their role in a sentence. This is called case, and it's primarily used with pronouns (see below).
Pronouns:
* Case: Pronouns have specific forms depending on their function in a sentence. There are three main cases:
* Nominative: Used for the subject of a verb (who is doing the action).
* Example: *I* went to the store. *He* is happy.
* Objective: Used for the object of a verb or preposition (who is receiving the action or is being talked about).
* Example: She gave the gift to *me*. The dog followed *him*.
* Possessive: Shows ownership.
* Example: *My* book is on the table. *Her* cat is fluffy.
Key Differences:
* Number: Pronouns usually don't change for number (except for a few special cases like "I" vs. "we").
* Case: Pronouns *always* change form depending on their case, while nouns do this less often.
In Summary:
* Both nouns and pronouns can change form, but primarily for different reasons: nouns for number and case, and pronouns mostly for case.
* Pronouns have a more complex system of case changes than nouns.