X-Bar theory is bogus

Noam Chomsky proposed the X-bar theory to explain describe a universal grammatical structure, common to all language.  An admirable objective.  The problem is, it's batshit crazy.  If you haven't heard already go and read the node above, I can wait.

Right, so the idea is that every part of speech is a "phrase", not just a word.  Some are almost always single words (called a head) such as noun phrases. "dog" is a valid example.  However all of them can be extended.  That is, in every situation where you need a noun phrase you can use a longer noun phrase.

Some phrases have a minimum length because they require other sub-phrases.  This is true for many verbs, specifically intransitive verbs.

"The quick brown fox jumps over a lazy dog" has two noun phrases ("the quick brown fox" and "a lazy dog"), some adjectival phrases ("quick brown", "quick", "brown", "lazy"), a prepositional phrase ("over a lazy dog") and a verb phrase (the whole damn thing).

Already this is starting to look like hard work, but that's fine, we're just being rigorous.  We can represent this sentence in the syntax tree that defines X-bar:

                         /  \                                     
                        /    \                                    
                       /      \                                   
                      /        \                                  
                     /          \                                 
                    /            V'                               
                   /            /  \                              
                  /            /    \                             
                 /            V0     PP                           
                /             |     /  \                          
               /              |    /    \                         
              /             jumps {}     P'                       
             NP                         /  \                      
            /  \                       /    \                     
           /    \                    P0      P'                   
         The     N'                   |     /  \                  
                /  \                 over  /    \                 
               /    \                     {}     NP               
              AP     \                          /  \              
             /  \     \                        /    \             
            /    \     \                     the     N'           
           {}     A'    \                           /  \          
                 /  \    \                         /    \         
                /    \    \                       AP     N0       
               AP     \    \                     /  \      \      
              /  \     \    \                   /    \      \     
             /    \     \    \                 {}     A'     dog  
            {}    A'     \    \                      /  \         
                   |      \    \                    /    \        
                   |       \    \                  {}     A0       
                  A0       A0   N0                         |      
                   |        |    |                        lazy    
                 quick   brown   |                                

There are lots of empty levels in this tree, but that's fine really, because we're allowing for all the possible ways you can slot words together, not just in English but in every conceivable language. There are plenty of weird things that have to be possible.

Wherein bombs are dropped

Some of you will have spotted the problem already, but don't feel bad if you haven't. It's a complex tree that you can't really fit in your mind all at once. I'll give you a clue, read the leaf nodes left to right. Yup, that is our complete, grammatical sentence. Doesn't that strike you as a bit odd? Well, it shouldn't really, as here is the problem. Although the tree structure is supposed to be universal people want it to do too much. They want it to define how words fit together semantics and syntax. Because they're greedy.

The upshot of this little decision is that for even moderately complex sentences the tree has to be completely re-ordered to make the leaf nodes read out correctly. Two sentences with identical meaning could be encoded with very different trees. The concept of an inflectional phrase allows us to move the subject to the top left of the tree so it's always first. Now, even the linguists balked at this, so they decided there was a difference between where a node is and where it came from. This is called "base generation", a phrase can logically belong in part of a tree, but move to another to meet word order requirements.

In other words, there are a series of meta-rules for this universal grammar that tie it to a specific language. This theory suddenly becomes hopelessly inelegant, the tree might as well be replaced with a list of words for all the value it adds.

The lesson

Two simple, complementary theories are better than one complex one.  By putting too much stock in this tree representation it becomes ordered and language-specific.  Instead of a universal grammar we get an overly complex representation of a sentence in a single language and a false impression of universality.

Don't be a fool, demand relational grammar from your linguists.