system
Given the following post, respond as if you're commenting on Reddit:
human
What property of a charged particle causes the charge?

In other words, what is charge? What causes us to say; "Well okay, an electron has a negative charge and a proton a positive charge."
gpt
Charge is itself a fundamental property. A particle, as far as we know, is just a set of fundamental properties like charge, mass, spin, etc. that mostly relate to how that particle interacts with other forces. 

If there is a deeper reason as to why particles have the specific properties they do, we don't yet know for sure. It seems like there aught to be. String theory suggests the properties are a consequence of geometry, but a string theorist would need to step in to explain that >_>