Subject

The Subject
Tests for identifying subjects in English:

• Agreement:
  In a finite sentence, the main verb agrees with the subject.
  Pat writes/*write letters to his friends.
  
• Tag question:
  The pronoun that occurs in a tag question refers to the subject. John wrote a letter to his sister, didn't he/ *she/ *they?
• Subject-auxiliary inverions:
  In forming a yes/no question, an auxiliary is placed directly before the subject.
  Will Pat write a letter?

Categories and structural position Only an NP or an S' can be the subject of a clause.
The subject of a clause S is the NP or S' that is immediately dominated by that S node and that precedes the VP (or AuxP) of the clause. Example:

         _S__
        /    \
     subj     \
      /        \  
    NP   ______AuxP________
   /__\ /__________________\
   Pat  will write a letter.

Read further on other grammatical functions:

1. The predicate
   
2. The subject
   
3. The complements
   
   1. The direct object
      
   2. The indirect object
      
   3. The predicative complement
      
   4. The oblique complement
      
4. Modifiers (Adjuncts)
   

  ← Predicate        ↑ Grammatical Functions          → Direct Object