Extended projection principle

The Extended Projection Principle (EPP) is a linguistic hypothesis about the obligatoriness of subjects. It was proposed by Noam Chomsky as an addendum to the Projection principle (which it has outlived significantly) in his book "Lectures on Government and Binding". The basic idea of the EPP is that clauses must contain an NP in the subject position (i.e. in the specifier of TP or IP).

The EPP has been used extensively to describe sentences where the phonetic subject is a dummy pronoun like "it" or "there." These words are often inserted into subject position when the main verb (or other predicate) of the sentence doesn't assign an "external" (i.e. subject position) theta role. Although they are vastly outnumbered by verbs which require meaningful subjects (cf. "kick" in "Tom kicked the ball"), many verbs do not.

The EPP states that no matter whether the main predicate assigns a meaningful Theta role to a subject, a subject must be present nonetheless. As a result, verbs which do not assign external theta roles will appear with subjects that are either meaningless (e.g. expletive "it," "there"), or ones which have been moved into subject position from a lower position (e.g. subject of an embedded clause).

Examples which have been said to be the result of expletive subject insertion by the EPP:

1. It seemed that John would never calm down.

2. It ( rains | snows | hails | etc. ) frequently in Quebec.

3. There seems to be a problem with the radiator.

Notice that in all of these the overt subject has no "referential" reading. This is not the case with the instances of "it" and "there" in examples 4-5, in which the main verb assigns an external theta role:

4. I went to pick my car up, but the mechanic said that it wasn't ready.

5. There would be a nice place to put the Rembrandt (said while pointing to a spot on the wall).

In his dialogue De ente, Plato states that there cannot be a sentence without a noun [subject] and a verb. [...] Aristotle teaches the same in Peri hermeneias 2 : 'Thus, a verb without a subject will mean nothing'." -El Brocense, 1587. This is an early formulation of Chomsky's Extended Projection Principle.

In languages that allow pro-drop (such as Spanish or Italian), the empty category pro can fulfill the requirement of the EPP.

McCloskey (1996) proposed that there is one group of languages that lacks the EPP; the VSO languages (like Irish), which appear to not only lack expletives, but lack movement operations triggered by the EPP>