I believe I’ve noticed for the first time a way in which modern English preserves a distinction between adjectives used attributively or predicatively. What’s that you say? Such terms never featured in your grammar education? How appalling!
One of the basic things you have to learn about adjectives in ancient Greek is when the adjective is simply modifying a noun (attributive) and when it is serving as a predicate (predicative). No big deal. In Greek the adjectives have the same morphology but are placed differently relative to the noun and the definite article.
Generally English doesn’t have nearly the same synthetic features that ancient languages do, and so it’s always fun (well, my kind of fun) to see where English still conjugates verbs (ever so slightly) or declines nouns (pronouns, relative pronouns), and the like.
At the lunch counter my Hispanic friend asked why some Anglos say “four foot, five inches” and others say “four feet, five inches.” After making a joke about one foot, two foot, three foot, four foot…, I decided to try to work out a rule. Bonus: when I posed the question about the rule to some of my students, one of them quickly worked it out on his own. So I must be right!
The rule: Units of measurement are “always” in the singular when used attributively; i.e., as an adjective simply modifying a noun. Units of measurement are “always” in the plural when used predicatively; i.e., when serving as the predicate of a sentence or clause.
I bought a twenty-five foot length of rope at the store.
The rope is twenty-five feet long.
This twenty-pound baby is breaking my back.
My son weighs twenty pounds or more.
Please hand me the 100 cubic centimeter flask.
The flask holds 100 cubic centimeters of liquid.
And so on. I’m pretty sure this rule applies to all units of measurement but is applied inconsistently when it comes to measuring the height of a person. Lots of people tend to one usage or the other when it comes to measuring humans, and lots of people freely shift between the two usages. But otherwise, I claim my rule is sound.
And sure, I probably could have looked this up in a textbook for teaching English to non-native speakers. But what’s the fun in that?