system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What is the best way to identify correctly if a song is in C major scale or A minor scale, because notes are all the same?
gpt
Tonal center. What feels like home base. 

If a piece resolves to C most of the time it's probably in C. If it goes back to Am it's probably Am. 

Example of a chord progression:

C C C G Am C is in C. 
Am Am Am F C Am is in Am.