Making Suggestions

Let's (do something.) and why don't (we do something?) have the same meaning. They are used to make suggestions about activities for you and me to do together. Each use the simple present for of the verb but can be used to speak about doing something in the future. Look at the following sentences.

1. Let's go to the movies.
2. Why don't we go to a movie?
3. Let's go to the movies next Saturday.
4. Why don't we go to the movies next Saturday.

In sentences 1 and 2 the person making the suggestions want to go to the movies now, at the time the sentence was spoken. In sentences 3 and 4 the person speaking is trying to set a date to go to the movies at some future time, (next Saturday).
Let's look at some more examples.

a.)
A: It's hot today. Let's go to the beach.
B: Okay. Good idea.
b.)
A. It's hot today. Why don't we go to the beach.
B: Okay. Good idea.

Let's = let us, but is not usually used in the non-contractive form unless the speaker is wants to be very formal.

People also use Why don't (you do something.) to make a friendly suggestion, or to give friendly advice.

c.)
A: I'm tired.
B: Why don't you take a nap.
C: That's a good idea. I think I will.

Note: You can not use you with let's.
Incorrect: * Let's you take a nap.