It is perfectly reasonable to want all sorted collections of X to have a canonical order, but to still allow people to consider equivalent items to be equal. T

It is perfectly reasonable to want all sorted collections of X to have a canonical order, but to still allow people to consider equivalent items to be equal. The example someone else gives with +0 and -0 is very good: in most contexts, those two should probably be equal (+0.equals(-0)), but when sorting a list, you might want all -0s to come before all +0s (-0.compareTo(+0) == -1). Given that Comparable is almost exclusively used for sorting, this is actually quite unlikely to cause problems in practice. Of course, it's a much bigger problem if you use entirely different concepts of equality. For example, a Name class where a.equals(b) only if they have the exact same Unicode code points, but where a.compareTo(b) == 0 if they have the same Unicode codepoints after normalization would be crazy. Edit: and of course BigDecimal from the example below does exactly this crazy thing...