An intermediate student of Chinese should be aware of the classic "shi... de" construction. It's important to learn and use. But don't be tempted to think that the "official" 是⋯⋯的 (shì... de) pattern is the only way that 是 and 的 can work together in a sentence! There are multiple ways to use 是 and 的 together, and they can be used for different purposes. This article helps break down the various uses of 是⋯⋯的 and tackle the confusion head-on.
This is the most simple way to use 是 with 的: you drop the noun and let 的 represent it. This usage requires context; otherwise the other person won't know what noun you are referring to. Once that is established, however, this usage is really easy: having the 的 take the place of the noun is sort of like the way we say "one" or "it" in English. It's a basic substitution, but it's one that is very common and very helpful in everyday Chinese. Some people consider this just to be a version of "Adjective + 的 + Noun" that has dropped the noun, so the 的 has to take it's place. The structure without the noun might take a little practice, but once you get it, it's so easy you'll be using it all the time.
If you're a good student, you learned the classic pattern for simple sentences using adjectives long ago (you know, the 你很漂亮 type), and you know that you're not supposed to use 是 in these sentences. But then you may have later come across some sentence patterns--apparently using adjectives--where you have to use 是 (and also 的). These are sentences that use a special type of word (you might think of it as a special class of adjectives, if that helps) called distinguishing words.
The bold words are the "distinguishing words," so pay attention to what sorts of things they describe.
This classic pattern is the one for emphasizing certain details about events in the past. It's often used to ask pointed questions about past events, and then to answer those questions. Usually, the situation is already established, and the speakers are trying to get more specific clarification, such as when, where, or how the action took place. When this is the case, the phrase that follows the 是 is the part of the situation that is being emphasized. It is also important to know that you can't use "了" in this sentence. "了" only tells you that the action is completed, not any of the other details that this construction is looking for. Since it is already understood that the action took place, the "了" is unnecessary. A more complete explanation of this particular usage can be found here.
The examples below share the theme: 我在上海学了两年中文. The bolded words are the aspect of the situation that are being emphasized.
In the example above, you might have noticed something funny with the object of the verb. In this construction, if the verb is transitive (it takes an object), then the object can be placed either before or after the 的 without affecting the meaning. Take a look at the example below:
When explaining "what you came for" or "what you want to do," it's common to use yet another type of 是⋯⋯的 construction.
When expressing a purpose, 是 and 的 are often used together with 用来, especially when the subject is a thing.
This pattern can also be used to talk about what kind of work people do:
Sometimes you can use 的 to really add a kick to your responses, making them stronger. You might even hear Chinese people reply with just 是的 which means "That's right." This usage is similar to the way that English speakers might stress the word "is" in sentences like "It is my food." When used to express affirmation, 会, 能, and 可以 are often used as well. Again, the 是 is optional.