Person A has $20 million. Person B has $19 million.
1) A is rich
2) A is not poor
3) A is richer than B
4) A is more poor than B
5) A is less poor than B
6) A is not poorer than B
7) A is no poorer than B
8) A is not as poor as B
9) B is rich
10) B is not poor
11) B is poorer than A
12) B is more poor than A
13) B is less rich than A
14) B is not richer than A
15) B is no richer than A
16) B is not as rich as A
(PS I later thought of A is the richer of the two, and I’m sure there’s more.)
At this point my brain started asploding. I have little chance of explaining the nuances of all these, but as a native speaker I instantly understand them when I hear or read them, and have no hesitation in using the right one in the right context. The Cambridge Grammar of the English Language has sections on ‘Equivalences and entailments’ and ‘Relative infrequency of comparisons of inferiority’, which cover some of this ground. Clearly, 1), 3), 9), 11) and 16) are the most standard. All the others are recorded, but Google Ngrams doesn’t give any context.
Similar comments apply to old/young and tall/short.
Things are even more complicated with hot/warm/cool/cold, even taking just -er and -est.
Location A is 35 degrees (centigrade). Location B is 25 degrees. Location C is 15 degrees. Location D is 5 degrees.
A is hot, hotter than the other places and the hottest place of the four.
B is warm. It is warmer than C and D, but also hotter than C and D. It is cooler than A, might be colder than A but it’s not *warmer than A. It’s not *the warmest place of the four.
C is cool. It is warmer than D, but it sounds strange to say that it’s hotter than D, and it’s not *cooler than D. It’s cooler and colder than B, and ?cooler and colder than A. It’s not the coolest place of the four.
D is cold. It is colder than the other places and might be cooler than C, but it sounds strange to say that it’s cooler than A or B. It’s the coldest place of the four.