This one was inspired by a client whose daughter was having a bit of trouble with the explanations she was being given at school. As he wasn’t sure how best to explain it, he came to the person he’s used to outsourcing writing stuff to: me. I was rather touched, actually – and I’m always happy to help where I can!
People do mix up bought and brought, and I presume it’s because they sound similar (see would have and would of) as they mean quite different things and come from quite different origins. These origins are the best way to tell them apart, actually
Bought and brought are both past tense words – so they’re used to write about things you’ve done in the past, before now.
Brought is the past tense of BRING. You might bring your Dad to the disco (and wish you hadn’t!) or bring an apple to school. If you did that yesterday, you brought your Dad to the disco, left him there, and then you ran away. You brought an apple to school this morning, and you might bring another one to school tomorrow.
Bought goes with BUY. You might buy a pair of shoes with sequins on today. Yesterday, you bought a pair with glitter on. Maybe your Dad bought your apple at the supermarket.
So if you spent money on something, you bought it. If you took it somewhere, you brought it along with you.
“Last week, I bought a bag of apples. I brought one of the apples with me to school every day that week.” – and it works just the same with other ways of writing about the past: “Last week, I bought a bag of apples. I have brought one of the apples with me to school every day this week” ; “I have bought a bag of apples every week for years”.
You can find more troublesome pairs here.