I’m having a debate with someone about what is considered an opposite.

We agree on obivious ones, up:down, fast:slow, on:off, etc.

The type we disagree on are things that I think are alternatives or are commonly paired, but are not opposites. The opposite of vanilla is NOT chocolate. The same thing with salty:sweet, solid:liquid, salt:pepper, cat:dog, sweet:sour, etc.

To be an opposite do the two words have to be diametrically opposed? What is the proper basis for calling two words opposites? The dictionary definitions I have looked up are pretty wishy-washy.

Any thoughts?

You’re trying to shoehorn a term into places it doesn’t fit. For many things there is no diametric opposite, the term just doesn’t apply. What would the opposite of dog be? A non-living, non-furry, invertabrate?

Don’t forget doesn’t bark.

I agree. There just isn’t an opposite for some things.

I do think that the opposite of sweet can be argued as sour though.

Oh, and a hearty welcome to SDMB levy96018a.

Interesting question the more I think about it. Look at the term binary. In computer terms a piece of information that can only be one of two choices is the smallest piece of information you can have. If a property is binary it can have a unambigous opposite. For most of the items you identified as having no clear opposite they are complex things with many properties.

[ul]:cool: [sup]The opposite of salty is inexperienced.[/sup][/ul]

I disagree. Sweet is one of five defined tastes with salt, sour, bitter and whatever the hell they call MSG if you count that one. I don’t think we need to get into a shelaliegh fight because I think “bitter” is more opposite to sweet but you see where I’m going I think. Same with liquid, just one of four common states of matter. I think those are more like asking what is the opposite of a particular temperature. What’s the opposite of 39º C?

north is just one of 4 defined primary directions ---- does it have an opposite?

You only need two directions to get the four we recognize. South is negative north, and west is negative east.

The five flavors, on the other hand, are orthogonal. None can be expressed as a combination of the other four.

Richard Wilbur, former poet laureate of the United States, wrote more than one book of poetry about this–the first was called “Opposites”–where he plays upon the essential ambiguity of what it means to be an opposite.

Here’s the first one:

What is the opposite of nuts?
It’s soup! Let’s have no ifs or buts.
In any suitable repast
The soup comes first, the nuts come last.
Or that is what sane folks advise;
You’re nuts if you think otherwise.

You’re not sane if you think the OP is resolvable. You agree that the opposite of fast is slow? Here’s what Wilbur says (#31):

**The opposite of fast is loose,
And if you doubt it you’re a goose,
“Nonsense!” you cry, "As you should know,
The opposite of fast is slow.
Well, let’s not quarrel: have a chair
And see what’s on the bill of fare.
We should agree on this at least:
The opposite of fast is feast.

Note, also, that even if slow is the opposite of fast, there’s a heck of a lot of middle territory that you miss that way. As far as driving speeds go, 45 mph isn’t fast, but it isn’t slow either. How will you deal with that?

it’s fast if you’re still in your driveway…

In Formal Logic, there are four sets of opposition:

Contradictory Opposition indicates two mutually exclusive properties, attributes, or whatever. This is generally indicated by the expressions subject and not subject (or non-subject).
Being and not being.
Man and not man.

Privative Opposition indicates the opposition between a form and the lack of that form in a subject capable of possessing it.
Manly and unmanly.
Sensitive and insensitive. (However, it would be improper to refer to a rock as “insensitive” because “sensitive” is not proper to the subject “rock.”

Contrary Opposition is an opposition between two positive terms signifying extremes of difference within the same subject, each of which excludes the other. Therefore it indicates mutually exclusive properties or attributes within the same subject.
Odd and Even (when used of numbers).
Intelligent and Stupid (when used of degrees of intelligence).

Relative Opposition indicates pairs that refer to each other when stated in opposition, and so indicate only a “relative” level of opposition within the subject.
Whole and Part cannot be used at the same time regarding a subject, but each uses the other to describe a difference in a property within the same subject.

Given those categories, I would not accept chocolate and vanilla as opposites.
Lest someone consider them as being in Contrary Opposition, I would note that chocolate and vanilla do not exist on a spectrum of flavors, with one denying the other, but as discrete flavors, in themselves. Chocolate may exclude vanilla, but ist does not create an exclusive condition for ice cream, which may have flavors that are neither chocolate nor vanilla.
Similarly, I would not think that they indicate Relative Opposition. Neither is defined in terms of the other.

I’d put bitter as the opposite of sour - acid is sour; alkali is bitter.