system
Given the following post, respond as if you're commenting on Reddit:
human
Why is there a critical point between liquids and gases but not between solids and liquids?
gpt
The critical point is the end of the coexistence curve. There is clearly one for liquids and gases, but it is not so clear in the case of liquids and solids.

If there were a critical point for solids and liquids, one would expect to have a region in phase space (for example, in temperature plotted against pressure) where the supercritical matter can change between solid and liquid without ever encountering a phase transition. 

Can a liquid continuously transform into a solid? We're not sure, it seems unlikely, and we haven't observed it.