Question

Use that for essential clauses that tell you exactly which person or thing you mean, as in "The book that has a red cover is mine." Use which for nonessential clauses that just add extra information and are set off by commas, as in "My bike, which is blue, needs a new tire." The difference is that essential clauses are needed to identify the noun and have no commas, while nonessential clauses only give extra facts and use commas. If you remove a which-clause the main idea stays the same, but if you remove a that-clause you might not know which thing you meant.
Shorten this paragraph

Answer 1

Use "that" for essential (restrictive) clauses that identify which person or thing — no commas (e.g., "The book that has a red cover is mine") — and "which" for nonessential (nonrestrictive) clauses set off by commas (e.g., "My bike, which is blue, needs a new tire"). Removing a which-clause leaves the main meaning; removing a that-clause can make the reference unclear.