Two approaches are discussed here: 

1. Prescriptive Approach
In this view, grammarians dictate the use of languages.
“Do not say this, say that, this is wrong, that is right” are the common phrases and statements in Grammar books written with this view.
Examples in English are:
You must not split an infinitive.
You must not end a sentence with a preposition.
“Traditional Grammar” is classified under this approach.

 

2. Descriptive Approach
In this view, languages are described the way they are used. There is no “must” and “must not” for language users. Having this view, we may introduce “Structuralist Grammar”. The main concern his grammar is to study the distribution of forms in a language. The method involves the use of “test – frames” that could be sentences with empty slots.

 I heard a  __________    yesterday.

Whatever fits in this slot is considered to be a “Noun”. By developing a set of test frames of this type, we can produce a description of “Sentence Structure” of a language

 

The weak point in structuralist analysis is that they do not pay attention to meaning. All they are concern of is “form”.  The grammar is not able to explain the oddness in the following sentences:

“The hamburger ate the boy.” or

“My cat studies Linguistics.”

 According to structural grammar these sentences are acceptable. There are NP+VP in each sentence and the constituents are acceptable. But they are still odd and we have to find an explanation.

Using “semantic features” might be a good help. We may consider some features for the constituents (verb and noun in this case) to avoid the oddness.

 The verb “eating” needs an animate subject and the verb “studying” needs a human literate subject. We can formulate this as follows:

The hamburger        ate          the  boy.

        [-animate]   [+animate]

            Semantic Crash

 

My      cat           studies         Linguistics.

       [-human]  [+human]

               Semantic Crash

 

 This incident is called “semantic crash”. That is, these sentences are  crashed  because of the semantic problems they have. A plus and a  minus cause semantic crash. This way we can explain the origin of  oddness.