Can pain be defined and can robots feel it?

To answer these questions requires sorting through a lot of interwoven beliefs or feelings. Where we think there is pain does not correlate with what we are reluctant to damage, and what we are reluctant to damage depends on the directness of the damaging.

Many of us eat dead cow, for example, but couldn’t bring ourselves to kill one. Similarly for capital punishment. Some of us sometimes wince with empathy when our cars are damaged, although often we think the car is not feeling pain. There may be a number of reasons why we think a car does not feel pain:

1) The car doesn’t scream or moan or bleed like a human.

2) The car doesn’t have a face like a human, and isn’t cute the way a human infant is.

3) The car doesn’t live a life with its own intentions or directedness.

4) The car was made by humans.

5) The car doesn’t have nerves and a brain like humans.

6) The car doesn’t have anything like the intellectual ability of humans.

A chimp, on the other hand, matches a human on all six points.

A dolphin more or less meets the first two, and certainly meets the last four.

Cows: more or less 1, more or less 2, 3, more or less 4, 5, more or less 6.

Human fetus: more or less 1, more or less 2, 3, not exactly 4, more or less 5, not exactly 6 (but 2,5,and 6, potentially).

3-toed sloth: more or less 1, more or less 2, 3, 4, 5, maybe 6.

Kitten: 1, 2, 3, more or less 4, 5, 6.

Fish (in wild): not exactly 1, more or less 2, 3, 4, more or less 5, maybe 6.

Chicken egg: not 1, not 2, 3, more or less 4, not 5, not 6, (but 5 and maybe 2 and 6, potentially).

Slug: not exactly 1, 2 with difficulty, 3, 4, 5 doubtful, not 6.

Bat: more or less 1, 2, 3, 4, 5, 6.

Tree or flower: not 1, not 2, 3, more or less 4 (degree varying), not 5, not 6.

Apple: not 1, not 2, not exactly 3, more or less 4, not 5, not 6.

Koala: more or less 1, 2, 3, 4, 5, more or less 6.

Personal computer: not exactly 1, not 2, not exactly 3, not 4, not exactly 5, maybe 6.

House fly: not exactly 1, not exactly 2, 3, 4, maybe 5, not exactly 6.

A.I.D.S.: not 1, not 2, 3, 4, not 5, not exactly 6.

A mouse of a patented variety designed for labs: more or less 1, more or less 2, sort of 3, sort of 4, 5, not really 6.

A possible robot: 1, 2, 3, not 4, 5, 6.

A robot produced by robots in a robot colony: 1,2,3,4,5,6.

In fact, we can imagine robots with all possible combinations of the six. Which combinations would count as sentience? Are there degrees of it? Am I missing relevant criteria? And if we can sort out what sentience is currently believed by most of us to be, should we continue to think of it that way? Why?