What is the difference between "used to" and "would"?

I was asked this recently: What is the difference between "used to" and "would"? Let's take a closer look at this.

When we talk about repeated actions or events in the past, especially when they no longer happen, we can use "used to":

I used to bang the pillows with a pair of drumsticks.

Most grammar books actually say you can use "would" instead of "used to" in this context, but take this example:

I would bang the pillows with a pair of drumsticks.

I wouldn't say it. Why? It doesn't sound natural. But, I would say this:

When I was a child, I would bang the pillows with a pair of drumsticks.

In this example, both "used to" and "would" sound perfectly natural. The difference now is that there is a time reference attached to the action.

More examples:

I used to write poems. Not: I would write poems.

I used to/would write poems when I felt lonely.

Sheila used to go for long walks.

When Sheila was living in Sydney, she used to/would go for long walks when the weather was good.

It is worth mentioning here that we often use would to talk about annoying habits:

I would bang on tables with my bare hands everywhere I went and that would drive everyone up the wall!

Note, however, that in questions, we won't use "would":

Did you use to play the drums when you were a teenager? (Answer: yes, I did -> I was in a band)

Not: Would you play the drums when you were a child?

The same rule applies to negatives:

Rob didn't use to sing much when he was younger (suggesting that it wasn't a habit he used to have).

Rob wouldn't sing when he was younger. (This implies that he refused to sing.)

When we talk about past states, we don't use "would":

I used to live in London, and I used to own a convertible.

We used to be computer programmers.

This building here used to be a fantastic cinema.

Complicated? My advice is to stick to "used to", and you won't go far wrong. Just remember that "would" means the same sometimes.