system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is the noun form of "unstable" written as "instability"? Why with the change of prefix?
gpt
You do not really derive "instability" from "unstable".  Unstable derives directly from stable, and instability is derived from stability which is derived from stable.  At no point does the un prefix transform into the in prefix.