aiga siktak moseorie meorireul buditchiji anhge josimhaesseo.

I was careful so the child wouldn’t hit her head on the corner of the table.

Breakdown of aiga siktak moseorie meorireul buditchiji anhge josimhaesseo.

• 아이: child
• ~를: object particle
• ~가: subject particle
• ~에: location particle

Questions & Answers about aiga siktak moseorie meorireul buditchiji anhge josimhaesseo.

What is the basic structure of this sentence?

It breaks down like this:

• 아이가 = the child
• 식탁 모서리에 = on/against the corner of the table
• 머리를 = head
• 부딪치지 않게 = so that they would not bump/hit
• 조심했어 = was careful

A very literal structure is:

[the child] [their head] [on the table corner] [not bump so that] [was careful]

In natural English, Korean usually packs the prevention idea into -지 않게 조심하다, which means to be careful so that something does not happen.

Why is it 아이가 and not 아이를?

Because 아이 is functioning as the subject of the clause 아이가 ... 머리를 부딪치다.

So the idea is not someone was careful with the child as a direct object. Instead, it is the child might bump their head, and the sentence is about preventing that.

That is why 가/이 is used:

• 아이가 머리를 부딪치다 = the child bumps their head

not

• 아이를 머리를 부딪치다 = ungrammatical

Who is the subject of 조심했어? Is it the child or someone else?