Specifier, Head, Complement—three important components of Generative Grammar—
1, Head
When we Merge verb- help and pronoun-him, we get phrase [help him]. The phrase [help him] thus attained is interesting, because this phrase can appear where verb appears, but can not appear where noun appears. Examples are as below.
I will help.
I will [ help him].
He is handsome.
[Help him] is handsome.
In this respect, the phrase [help him] behaves like a bigger verb. When you attach noun or pronoun to the verb like help, you get an extended verb. The preceding verve decides how the attained phrase behaves. In this case, verb- help is said to be the Head of the projection. The phrase [help him] is like a kind of extended verve, so [help him] is called a projection of Head word-help.
2, Complement
Constituents which Merge with Head are called complements. Complement does not determine the category of the phrase. For example, when Head-help and Complement-you Merges, the attained phrase [help you] has category of Verb Phrase. In this respect, pronoun-you has no role to decide what category the phrase [help you] belongs to. You Merge Head and Complement to get a projection. The Head is the constituent which decides the overall category of the projection. The complement is the constituent which does not decide the overall category of the projection.
For example, when you Merge verb-kill and pronoun-him, you get phrase [kill him]. The phrase you get behaves like a bigger verb. So, in this case, verb-kill is Head. Pronoun-him is complement.
You cannot Merge whatever constituent you like with a given Head. Head-verb kill apparently choose what it takes as its complement. You cannot Merge adjective-tall with the head-kill. *kill tall. You cannot Merge verb as complement with the head-kill. *kill do. In this way, the head-kill chooses what it takes as its complement. Verb kill can take only pronoun or noun as its complement.
3, Specifiers
When you Merge verb-help and pronoun-him, you get [help him]. In this phrase, verb-help determines the category of the overall phrase, so verb-help is the Head, and pronoun-him is complement. Thus the phrase [help him] is projection of the head word-help. [help him] is a Verb Phrase/VP.
VP[help him] is Merged with Tense-will. The attained phrase [will help him] is the projection of Head word-will. So, this is projection of Tense constituent-will. But [will help him] is not a constituent. A constituent can be used by itself and can be understood. For example, VP[ help him] can be used on its own and still can be understood. But [will help him] is somehow incomplete. We need a subject.
Tense auxiliary verve- will has EPP feature. EPP feature is an acronym of Extended Projection Principle feature. A constituent which has an EPP feature needs specifier. When you Merge head and complement, you get a phrase which has the same category as head butt which is bigger than head. Such phrase is called projection of head. When you Merge specifier with this projection, you get even larger projection of head. When head has such projection, this projection is called Maximum Projection.
Head Merges with complement to create unitary constituent [head complement]. In VP, head is verve like help and kill. Complement is pronoun or noun. When you can Merge this projection with specifier and create another projection which has same head, the constituent [specifier [head complement] is Maximum Projection. Constituent consists of head and complement is called intermediate constituent. Intermediate constituents are indicated with “-“. This is pronounced as “bar”. So, [will help him] is T-bar. When you Merge appropriate constituent as specifier with this T-bar, you get Maximum Projection TP.
In this case, nominative pronoun or noun which has +human property can act as appropriate subject of T-bar [will help him]. So, when we Merge first person pronoun nominative case-I, we get grammatically correct phrase TP[ I will help him].
