Since vs Until

Did you know that until and since mean two different things?

They are both used as prepositions (tells you when something is happening in relation to something else) and conjunctions (joining words) but cannot be used instead of each other in a sentence.

Since

Refers to the time when the event or action began or when the event or action has already ended.

Until

Refers to the time when the event or action ends or the event or action is yet to happen.

Let's look at some examples to help illustrate this:

I have worked for the X organisation since 2012 (correct)

I have worked for the X organisation until 2012 (incorrect)

The second sentence is grammatically incorrect in two ways.

Using until suggests that the speaker has already left the organisation, in 2012.

However, using "I have worked" suggests that the speaker still works there. If we want to keep the word until then we need change the beginning of the sentence:

I worked for the X organisation until 2012 (correct)

Let's look at another example:

I cannot play on my Nintendo until I have done my homework. (correct)

I cannot play on my Nintendo since I have done my homework. (incorrect)

Again, the second sentence is grammatically incorrect in two ways.

Using since suggests that the homework has been completed, however the negative statement at the start of the sentence "I cannot play" suggests otherwise. If we want to keep the word since then we need to change the beginning of the sentence:

I can play on my Nintendo since I have done my homework. (correct)

A final example:

I haven't drunk coffee since last Wednesday. (correct)

I haven't drunk coffee until last Wednesday. (incorrect)

The second sentence is incorrect because the word until is used to refer to an event yet to happen. If we want to keep the word until we need to change the first part of the sentence. This needs to show that up until the point in time the speaker is talking about (last Wednesday) the event was yet to happen:

I hadn't drunk coffee until last Wednesday. (correct).

This means that last Wednesday was the first time the speaker had ever drunk coffee.