The dust (settle or settles)

Question

There is the idiom "the dust settle(s)" which is used to indicate that after an argument or big change, the situation becomes calmer. The question is that why the verb "settle" varies in different structures? Please have a look on the following sentences:

1. Let the dust settle!
2. When the dust settle's'...

**Example 1:

• We should let the dust settle from the recent scandal before we make any major policy decisions.
  

**Example 2:

• We should only start painting when the dust settles after construction is finished.

Answer 1

The construction "let + object + verb" takes its verb in the bare infinitive form. This is similar in structure, although not necessarily in meaning, to modal verbs which take main verbs in the infinitive (he goes; he must go).

The dust settles.

Here, "settles" is the correct conjugated form of the verb "settle" (for the subject "the dust").

Let the dust settle.

Here, the "let" construction requires a bare infinitive, which is "settle."

This may make it clearer:

• He is. Let him be.
• They are. Let them be.
• I am. Let me be.

Answer 2

Don't get distracted by the idiom - this is completely standard English syntax.

When we use the verb let, the next verb should be a bare infinitive.

Ex:

The girl sat down
We let the girl sit down

The boy goes home
Let the boy go home

The dust settles
Let the dust settle

The noun dust is a mass noun, like water - it refers to an uncountable amount of a substance. Like other mass nouns, dust is treated as a singular noun.

Ex:

The water is warm
The rice goes in the pot
The dust settles

Answer 3

“Let the dust settle” is imperative, where the main verb is always in the same form as the bare infinitive.

“The dust settles” is present simple, so it gets the “-s” for third person singular.