Apologizing

If you're human like me, chances are you'll probably screw something up at some point in your life. When you do, you'll probably want to apologize, and that's where this grammatical structure comes in handy.

The て form plus すみませんでした can be used to form an apology for something you've done. ごめん can also be used for more casual-sounding apologies.

本を忘れて、すみませんでした。
I'm sorry for forgetting your book.

居間を壊して、すみませんでした。
I'm sorry I destroyed your living room.

お兄さんを打って、ごめん。
Sorry I punched your brother.

逃げて、ごめん。
Sorry I ran away.

The negative て form can be used to apologize for something you didn't do. This is created by first conjugating to the plain negative, then removing the い in ない and adding くて.

秘密を教えなくて、すみませんでした。
I'm sorry I didn't tell you the secret.

蚊を殺さなくて、ごめん。
Sorry I didn't kill the mosquito.

One thing that's important to note is the usage of すみません. In actual conversation, my understanding is that most people use すいません instead, because it's faster and more natural sounding. So when apologizing, すいません can likely be used to avoid sounding a bit stiff.