What's the difference between THAT and WHICH?

The usage of that and which causes confusion, not only for students learning English as a second or foreign language, but also for native speakers of English.  Therefore, this topic can be a bit complicated for any speaker of English...The following will help clarify the major difference between the two: 

 

THAT

• That is used to describe essential information, necessary to express the meaning of the sentence.  The grammatical term for this is restrictive.  (Note: That always refers to the word preceeding it.)

Examples:

1. The house that was built by my grandfather built now belongs to another family in Nebraska. 
2. The woman that spoke at the conference yesterday gave me some useful information for our next project.

WHICH

• Which, on the other hand, is used for nonessential or extra information, not necessary to complete a sentence.  Commas are used with which but not with that.  This is referred to as non-restrictive.  (Note: Which can refer to the word preceeding it OR to another word in the sentence.)

Examples:

    1.

• The house that was built by my grandfather now belongs to another family in Nebraska, which is now worth three times as much.  (which refers to house) 
• The house that was built by my grandfather now belongs to another family in Nebraska, which is a state in the Midwest.  (which refers to Nebraska) 
• The house that was built by my grandfather now belongs to another family in Nebraska, which is a real shame.  (which refers to the belonging to another family.)

    2.

•  The woman that spoke at the conference yesterday gave me some useful information for our next project, which will start in one month. (which refers to project)
• The woman that spoke at the conference yesterday gave me some useful infomation for our next project, which I really appreciated. (which refers to the woman giving me info)
• The woman that spoke at the conference yesterday gave me some useful information for our next project, which I will pass along to our colleagues. (which refers to information)