* Subject: The subject of a sentence is the person or thing performing the action. It's the "who" or "what" doing something.
* Direct Object: The direct object is the person or thing that receives the action of the verb. It's the "who" or "what" being acted upon.
Think of it this way:
* The cat chased the mouse.
* Subject: Cat (performing the action)
* Direct Object: Mouse (receiving the action)
Since the subject is the one doing the action, it cannot also be the one receiving it.
However, the same noun can be used for both the subject and the object in different sentences.
For example:
* The cat scratched the table. (Subject: cat, Direct Object: table)
* The table was scratched by the cat. (Subject: table, Direct Object: cat)
In this case, "cat" is the subject in the first sentence and the direct object in the second.