Why is は used instead of の in this sentence?

for this sentence


why is it not


I am confused because we are talking about Tom’s feet as a possession, so it makes sense to me to use の instead of は

help is appreciated, thank you!


The short answer is Japanese and English are not 1:1.

edit: it seems you already got a couple of longer answers, just wanted to add that トムの足が早い is a perfectly valid sentence.


Like @ThousandJP said, Japanese and English are not 1:1. 足が早い is an expression in Japanese that can mean “to be fast (at walking or running).” Since 足が早い is an expression we’re not talking about Tom’s feet as a possession here, but rather using the expression to describe Tom as being fast. And actually, I think 足が早い is an い-adjective as a whole, in which case makes sense why の can’t be used.


What @josh said is correct, but I’d like to add the following.

トムは足が早いよ, could be translated as “Speaking of Tom, feet are fast”, there is no doubt that the feet are Tom’s feet.

足が早い it’s a common expression and “could be” considered as an i-adjective because it’s show as a quality. According to jmdict, 足が早い is “to be fast at walking and running” (quality/adjective). So its correct to say, トムは足が早い (“Tom is fast at walking and running”)


This topic is very briefly brought up in Genki I p. 172, if you’re by chance using that textbook. But either way, some great answers already in this thread! Thanks everyone.


thank you all for the replies, you are awesome!

from my understanding, トムの足は早い makes sense,

while トムは足が早い is more natural to use

is that right?

Hello. It’s funny but the use of が sounds natural to me. In the Spanish translation of the Illiad, Achilles is called “el de los pies ligeros”, “he of the light/nimb feet”. This comes naturally to my mind when I see “足が早い”.

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Edit2: 足が速い would be preferred in this case. 足が早い Goo Dictionary

Long version:
You are on the right track that トムの足が速いよ would be a valid way to express that Tom’s feet are fast. Instead of being one or the other though, both of those sentences express the same basic information. The difference is in that the は particle has the function of making the word it is attached to, the topic.

Comparing these two sentences:
Tom’s feet are fast.
Topic: None, Subject: Tom’s feet (トムの足)

As for Tom or On the topic of Tom, (his) feet are fast.
Topic: Tom. Subject: Feet (足)

The information is the same but there is a slight difference in nuance, so which would be more natural depends on the situation. For now, it should be sufficient to treat the の version as a plain statement of information and the は version as having a focus or spotlight on Tom.
Edit: I should add that it is common to consider トムは足が速い to be more natural because people tend to put the focus on the person when talking about their attributes.