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In the following sentence, are the words that and which interchangeable? In general, where to put that and where to put which?

The sentence:

At the end of this course, students will be able to

  • Analyze circuits that function as filters.

  • Analyze circuits which function as filters.

marked as duplicate by anongoodnurse, Robusto word-choice Jan 26 '15 at 23:27

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"That" and "which" are never interchangeable! The word "that" is used when the phrase that it starts can not be omitted from a sentence that contains it.

The word "which," which can be very useful, starts a phrase that can be omitted from a sentence without changing its meaning, and is almost always preceded by a comma.

Neither of your examples are complete sentences, but they can be illustrative:

He must analyze the circuits that function as filters.

Means that it is specifically those circuits that function as filters that it is he must analyze.

He must analyze circuits, which function as filters.

Means he will be analyzing circuits, and those circuits also happen to function as filters.

  • The sentence is an item of a list which begins with: At the end of this course, students will be able to: ... – AboAmmar Jan 26 '15 at 22:57
  • @AboAmmar So you are talking about a specific type of circuit, in that case, you would use "that." – Dmitri Jan 26 '15 at 22:59
  • Yes, it is the same meaning as your first example. Thanks. – AboAmmar Jan 26 '15 at 23:02
  • 1
    I think maybe you're being a bit dogmatic in stating that "'that' and 'which' are never interchangeable (!)". Can you support this position? We must address the motives which drive States to acquire weapons to defend themselves. Address to the UN. These examples are not rare. – anongoodnurse Jan 26 '15 at 23:24
  • @medica Just because it exists, does not mean it is right. I am not sure who is addressing the UN in this instance, but if she wanted to be grammatically correct, she should have used the word "that" instead of "which." Those are two distinct words that have distinct meanings---they are not synonyms---and etymologies; just like "red" is never "blue," "that" is never "which." – Dmitri Jan 26 '15 at 23:32

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