Pronouns and subjects
For many words, its location in the sentence is the main clue we have that it is the subject of the verb. However, with other words like the personal pronouns, they also change their form depending on their case, and this change gives us another clue.
For example, English has a third person pronoun. In other words, we have a word that refers back to an antecedent that is third person. (Do you remember our discussion above?).
This pronoun changes its form depending on its case (as well as its gender and number). (For our example, we will use the form that is masculine singular.)
If the pronoun is the subject of the verb, it will appear as "he".
If it is not the subject, it will be another form such as "him."