Word Usage – Difference Between Conjunctions ‘Why’ and ‘When’

1. In the first example "the" is used because of generalizing. When you generalize about something (an object, an animal), you use the definite article before it if it is a singular countable noun. Some other examples would be:

The horse is a mammal.

The telephone is a useful invention.

Notice than uncountable nouns are used without an article in this case:

Milk is good for you.

2. In the second example "last time" sounds similar to "last week" or "last month" and that is why many people would not use "the". Compare, however, these two sentences:

He said something completely different last time.

The last time we met he said something completely different.

In the first example"last" means "previous, the one closest to the present", and is similar to the use in "last month, last week". In the second example we use "the" because it is the last in a specified period of time or within a specified group of events. The difference would be more obvious here:

We met last Friday.

This is the most recent Friday.

The last Friday he was here we went to the museum.

This is not the most recent Friday, but the Friday, which was last of all the Fridays he was here.

I should point out, 2a and 2b both would be more natural to me if you used "very" instead of "much" -- "much worried" is not typical.

I don't claim to be representative of all speakers, but the use of "last time" to replace "the last time" sounds okay in both of these examples. I think it's much better in the first one than the second though--while I might expect to see 2b in casual speech, it would seem like swallowing or skipping over the "the" rather than something I know I would write.

Some web examples of the usage include a Facebook group called "Last time I heard that, I laughed so hard I fell off my dinosaur!!!!!" (...for whatever that's worth as evidence) and the headline of this Yahoo! news article. I think that's enough to show that it's recognized as legitimate by the average US English speaker. It also seems to come up a lot in song lyrics. But it seems most natural to me if it's at the beginning of a sentence.

In conclusion: when in doubt, use "the", and you won't be wrong. But I think you're right that you can probably omit it in many cases.