To make it simpler because often on the internet many examples are confusing. You use which if there are plural items OR the clause can be considered as plural. And you use that for singular items or the clause can be consider as singular. You also use which when asking a question about a choice of more than one possibility. "which answer is correct" "there are Three options of which I prefer option two" "last week I learnt/learned a new subject THAT I did not know before" = singular subject THAT I learnt/learned http://www.writersdigest.com/online-editor/which-vs-that Our office, which has two lunchrooms, is located in Cincinnati. Our office that has two lunchrooms is located in Cincinnati. These sentences are not the same. The first sentence tells us that you have just one office, and it’s located in Cincinnati. The clause which has two lunchrooms gives us additional information, but it doesn’t change the meaning of the sentence. Remove the clause and the location of our one office would still be clear: Our office is located in Cincinnati. visit this page scroll down to the example sentences. read them and understand. THEN this is most important IGNORE THE REST OF THE PAGE IT WILL CONFUSE AND BEWILDER YOU It is simple if you ignore the part of the page that is being reproduced here. That I have seen confused thousands of learners.

For example. My bike that has a broken seat is in the garage.In this sentence, you understand that the speaker has at least one other bike. (we do not know the owner has one bike or more than one.) it could be saying only one bike of mine that I own that is in the garage. Not sure this is a good example! ?

Lyuaza’s explanation is correct. It is great if you can use “that” and “which” correctly, but don’t worry too much about it. 90% of American English speakers don’t understand the difference.

In a defining clause, use that. In non-defining clauses, use which. If you can remove the clause without destroying the meaning of the sentence, the clause is nonessential and you can use which. For example. My bike that has a broken seat is in the garage.In this sentence, you understand that the speaker has at least one other bike.  Another example. My bike, which has a broken seat, is in the garage. Here, the broken seat is simply a description of the bike in the garage. There’s no implication that the speaker owns more than one bike.  i found this explanation on the Internet.

In a defining clause, use that. In non-defining clauses, use which. If you can remove the clause without destroying the meaning of the sentence, the clause is nonessential and you can use which. For example. My bike that has a broken seat is in the garage.In this sentence, you understand that the speaker has at least one other bike.  Another example. My bike, which has a broken seat, is in the garage. Here, the broken seat is simply a description of the bike in the garage. There’s no implication that the speaker owns more than one bike.  i found this explanation on the Internet.