Human: How do I know when to use the word "that" vs. "which"? Assistant: 
That is a tricky one, because it depends on the context of your sentence. Generally speaking, you should use that when you are referring to something specific, and which when you are not. For example, if you say “I have a dog, which is white,” then you are using which. However, if you say “I have a dog, that is white,” then you are referring to a specific dog.