Discussion Groups / English Usage / January 2007

It could, I suppose, but the phrase is so entrenched as meaning not
judging something because it *doesn't* appear to be good that the
usage would be confusing at best.

With the proper context, you could use it to mean either.  Unless you state
otherwise, though, I would assume you meant that the cover doesn't do
justice to the content.

Consider this song by Willie Dixon.  Notice that the sense is the
opposite of what you suggest:

You Can't Judge A Book By The Cover
(Willie Dixon) 1962

You can't judge an apple by looking at a tree,
You can't judge honey by looking at the bee,
You can't judge a daughter by looking at the mother,
You can't judge a book by looking at the cover.

Oh can't you see,
Oh you misjudge me,
I look like a farmer,
But I'm a lover,
You can't judge a book by looking at the cover.

Oh come on in closer baby,
Hear what else I gotta say!
You got your radio turned down too low,
Turn it up!

You can't judge sugar by looking at the cane,
You can't judge a woman by looking at her man,
You can't judge a sister by looking at her brother,
You can't judge a book by looking at the cover.

Oh can't you see,
Oh you misjudge me,
I look like a farmer,
But I'm a Lover,
You can't judge a book by looking at the cover.

You can't judge a fish by lookin' in the pond,
You can't judge right from looking at the wrong,
You can't judge one by looking at the other,
You can't judge a book by looking at the cover.

Oh can't you see,
Oh you misjudge me,
I look like a farmer,
But I'm a lover,
You can't judge a book by looking at the cover.

(c) Hoochie Coochie Music (BMI)

As above.

I'm going to disagree with the others and say that it certainly can be
used both ways, in particular to imply that something looks good but is
bad or rotten inside. That's the whole point -- "appearances are
deceptive," which is another common way of putting it. All kinds of
appearances.

A handsome young man with fancy clothes and a flashy car might look
appealing to a young woman, but her family and friends might know that
he is vain, selfish, a cheater, etc., and so caution her not to be
fooled by his good looks (the book's cover) but instead to judge him by
his actions.

The proverb isn't just one way, only that good things may look dull or
ugly. It definitely can mean that (visually) appealing things may be
hollow or bad. Surely this is no news to people here.

I wonder if this is about the difference between judgement and
prejudice. (The regular kind of prejudice, before it was limited to
racial discrimination.)

This proverb is usually repeated with the indefinite article,
not the definite, viz.:  "Don't judge a book by its cover."
The meaning is the same, a warning against superficial
impressions, but the proverb applies to any book (or idea
or topic), not to only one definite item.