There were a lot of great answers here. I gave the checkmark to ento's answer because I felt it most completely explained all aspects of this use of こと. But many of the other answers are excellent, so if you're visiting this question for the first time, please take a few moments to read through all answers. Thanks to everyone for your help with this question.
When learning the phrase "I like X", everyone learns "Xが好きだ". But if X is a pronoun, you sometimes see こと:
あなたが好きだ。 → あなたのことが好きだ。
What purpose does こと serve here? I know that in subordinate clauses, こと can eliminate ambiguity:
彼が好きな人 "a person he likes" or "a person who likes him"
彼のことが好きな人 "a person who likes him"
But in a simple statement such as the first example above, it doesn't seem to change the meaning at all.
My own searches on this problem have yielded the following two theories (neither with anything to back them up):
- こと adds a layer of indirectness, and is therefore preferred from a Japanese standpoint.
- こと encompasses more of the object ("you" versus "all the things about you")
Is either of these correct?
こと also shows up in many other situations, seemingly without any effect on the meaning:
事件を覚えている。 → 事件のことを覚えている。 I remember the incident.
地球を考えて行動する → 地球のことを考えて行動する take action while considering the
Earthplanet (edited to "the planet" to fulfill the requirement for 考える to be paired with something abstract)
What's going on here?