[retsibsi]

> And how do you define pain and pleasure?

They're not reducible, but I don't know if that means we don't have definitions; we can describe them well enough that most people (who aren't p-zombies or playing the sceptical philosopher role) know pretty well what we mean. All of our definitions have to bottom out somewhere...

> Do insects feel pain?

Nobody (except the insects) can know for sure. Our inability to know whether X is true doesn't imply X is meaningless, though.

[echoangle]

But how can X be a good indicator for something I want to determine if I can’t measure X either?

[retsibsi]

> But how can X be a good indicator for something I want to determine if I can’t measure X either?

In the comment that started this subthread, qsera was responding to someone who said "Imo we don't even have a definition of [consciousness]". If qsera meant that we can measure consciousness in terms of pleasure and pain, then of course I agree that they were just pushing the problem back a step. But I don't think that's what they meant.