What does “not as [adjective] as him” imply?

If it is written that X is not as tall as Y, it indicates that X and Y have unequal heights. But does this necessarily imply that X is shorter than Y?

Solution 1:

In the absence of further elaboration, yes: "I am not as X as you" implies that you have more X-quality than I do. If X is "tall", then I am shorter than you.

It is possible to follow up for a humorous (or insulting) reversal of the normal implication:

I am not as good as he is... I'm actually way better.

But if you don't do this explicit countering, the default reading is that "not as X as" is always "less X than".

Solution 2:

Logically, I do not think it should imply X is shorter than Y.

The definition of "as" according to Dictionary.com is

to the same degree, amount, or extent; similarly; equally

So, if I were to say "X is as tall as Y." I would be saying that X is equally as tall as Y.

If I were to negate that statement, then I would have "X is not as tall as Y." Which would be saying that X is not equally as tall as Y.

However, in general speech, I do agree with Hellion that it implies X is shorter than Y.