why does 人気 mean ‘‘popular’’ and also ‘‘sign of life’’. how do people know which reading do they have to use?
context is your best pal here … that and one been an adjective the other a noun helps too.
Maybe it helps to compare with English words like lead?
“This bar is made of lead”
“Where does this door lead?”
Different meaning and pronunciation, same spelling.
Much more likely to mean popular, but yeah, use your best judgement!
If you read a sentence and go “what the hell was that supposed to mean” then it’s a good idea to check that there weren’t any words like this.
As for the “why,” it’s because throughout history people got creative with kanji. They might use a kanji that was better known and had the same pronunciation until the kanji actually took on a new meaning. Then when the kanji got imported to Japan, the kanji get matched to Japanese words as well as the original loanwords. So you can end up with very different meanings and readings mingling.
For instance, the original meaning of 北 was “back.” It’s a drawing of two people facing away from each other. But in Chinese that word for back had the same pronunciation as “north” and it was used in its place for that. Eventually, north took over and they invented a new kanji to take over for “back.” 背.
But in the word 敗北 (はいぼく, defeat), the back meaning, abstracted to “turn away,” still survives.
The door leads to the bar!
oh, it reminds about such part (from rusty memory):
oi, John, lead this fella along this phase lead till the lead pipe breakage. don’t forget to take that black lead and apply it when connecting pipes, and be sure to match lead on this new pipe with broken pipe’s one.
and the bathroom is to the right, right?