Difference Between “Which” and “That”

In general – “which” is used to DESCRIBE a phrase.

“That” is used to restrict the scope of what you are talking about.

For example, 

“I’m going to the park that has tennis courts.”
instead of
“I’m going to the park, which has tennis courts.”

You can assume there are lots of different parks. Which park are you going to? You’re going to the one THAT has tennis courts.
When you are restricting the scope of ALL PARKS down to a specific one–then you use THAT.

Here’s another example:
“I’m going to Mountain Lake Park, which has tennis courts.”
instead of
“I’m going to Mountain Lake Park that has tennis courts.”

Here, “has tennis courts” describes a specific park Mountain Lake Park. It does not restrict the scope of parks because the scope is already restricted by giving a name to the specific park we are talking about. Since the phrase “which has tennis courts” is a DESCRIPTION that is NOT RESTRICTING the scope of our perspective, then we use “which” instead of “that.”

For more examples, watch these two videos here.

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