To my understanding, the は particle has a nuance of comparison. When is it applied though? Surely 私は猫好き… doesn’t have the meaning of comparison? Or does it?
It does, in a way, contrast “I” from “not I”. You’re not saying anything about whether someone else likes cats.
But yeah, the comparative element is more overt when there’s an actual comparison. 私は猫が好きですが、ボブさんは好きじゃないです。
It is why you need to be a bit careful about the use of は, though. If you tell a girl 今日はきれいです, they’re going to get offended, because you’re implying that they didn’t look pretty on other days.
“Today you look beautiful”.
Troublesome thing to say in English as well. No matter on what word one puts the emphasis
“You look beautiful today” is a very normal thing to say in English, and it doesn’t carry the same implication that the Japanese version does aha.
Well, if you lean into the word today then it would, as implied by putting は after 今日.
Honesty, the easier way to notice the “contrastive” usage of は is with its literal translation. ~は is literally something like “as for ~”. So, if we take the sentance “わたしはきょうはとうきょうへいきます。”, it literally translates to something like “As for me, as for today, I went to Tokyo.” Obviously this sounds strange in English, but it sounds fine in Japanese. With this sentence, the は acts as a qualifier. You imply that while you may have went to Tokyo today, but didn’t some other days. Why else would you need to qualify it with “as for today” if you didn’t?
This can also be done with just a single は as well. “ぎゅうにくはいい” could imply that while the beef is good, the other meet at the restaurant you are eating is not good. It also may not. It depends on the context and how it’s said. If は is emphasized, then it is definitely used contrastively. If not, then you need context.
Right I see. Just a side question, for the sentence “私は今日はとうきょうへいきます” I know it’s odd, but would it be wrong to say “今日が” as if to put emphasis that TODAY specifically it went to Tokyo?
今日が is not grammatical for this sentence. Your は in that sentence as you wrote it would already be seen as a contrastive は.
A lack of は (just 今日) would be a neutral way to write it.
It calls attention to whatever it follows as a topic of conversation. In many cases, this dovetails with what acts as a grammatical subject as well, so it doesn’t appear contrastive. But when you append it to places where it isn’t strictly necessary (following prepositional particles like に or で, temporal markers like 今日 or 時, etc.), it has the tone of calling special attention to those circumstances (much the same way “as for~” would in English), which is at least an emphasizer, but often, in context, contrastive to something that’s come before.