Earlier vs. before

[banderas]

Are they always interchangeable? When are they not?

[Clark]

Are they always interchangeable? When are they not?

Early may function either as an adj or an adv. (Earlier is the comparative degree form)

Before functions as a preposition, as a conjunction or an adverb.

As you can see they overlap only when used as an adverb.
e.g. Why didn't you come earlier / before?

But: Can we meet at an earlier hour? (adj)
Can we meet before lunch? (preposition)
Can we meet before you leave for London? (conjunction)

[svartnik]

Are they always interchangeable? When are they not?

before: preposition adverb, conjunction
earlier: adverb, adj

I met her before Christmas. -- before Christmas = time adverbial, before = preposition
I met her earlier Christmas. --

Before I met her, I did not know her. -- before = conjunction; the temporal clause modifies the whole main clause
Earlier I met her... --

I never saw her before. -- before = adverb, modifying 'saw'
I never saw her earlier. -- earlier = adverb

In earlier times -- earlier = adjective, modifying times
In before times --

[bhaisahab]

I never saw her before. -- before = adverb, modifying 'saw'
I never saw her earlier. -- earlier = adverb. Earlier than what?

[engee30]

e.g. Why didn't you come earlier / before?

That question (with earlier) can well be interpreted as:

• 1. Why did you come late? or Why did you come only minutes before the meeting? etc.

• 2. Why was it the first time you had come there? or Why had you never come there before?

With before, it's only option 2 that is possible.

[Clark]

That question (with earlier) can well be interpreted as:

• 1. Why did you come late? or Why did you come only minutes before the meeting? etc.

• 2. Why was it the first time you had come there? or Why had you never come there before?

With before, it's only option 2 that is possible.