Grammar 101 with Michael Kwan

We use a great variety of terms in the English language over the course of regular conversation. Many of these terms we may bring them up while speaking with one another in person or on the phone, but we may not use them in our writing nearly as often. As a result, many people may mishear and consequently misspell these terms. That’s how we arrive at an alternative motive or a bad rep.

Today, we highlight one more example of this phenomenon. If a plan couldn’t possibly go wrong, is it foolproof or is it full-proof?

A friend of mine on Facebook sent me the post below and the two of us collectively shook our respective heads. The correct term to use in this instance is foolproof. It is sometimes hyphenated as fool-proof, but the conventional and more widely accepted spelling is as a single word.

Foolproof or Full-Proof

Used as an adjective, foolproof means that something is infallible. It is incapable of going wrong. A plan that is foolproof is one that is made in such a way that nothing can go wrong. There is no risk of failure. In a much more literal sense, something that is foolproof is invulnerable to fools in much the same way that something that is bulletproof is impervious to bullets. A waterproof device cannot be harmed by water.

But if foolproof is the correct term, why would someone want to use full-proof instead? From a logical or mathematical perspective, you could argue that a “full-proof” plan is one that has been thoroughly tested. This use of “proof” is the same as in the word “proofreading” or providing a mathematical “proof.” In this way, you could say that something that is full-proof has been shown to be free from error.

That may make some logical sense, but it’s still wrong.

You might even look into the context of alcoholic beverages. A spirit that is full-proof (“100 proof”) is actually closer to 50% alcohol by volume. That’s why drinks like Bacardi 151 exist; it’s 151 proof, which works out to just over 75% alcohol by volume. In this context, “full-proof” isn’t incorrect, but if you want to talk about something that is infallible and impervious to failure, you want to use the word “foolproof.”

Drinking copious amounts of full-proof alcohol is a foolproof way to get intoxicated.

As an aside, the Facebook post above contains a second error. Even if “full-proof” were the correct term to use, it should not be capitalized based on how the rest of the title has been formatted. The “20” is the first word in the line, which could be spelled out and capitalized as “Twenty” if the writer preferred. Alternatively, the entirety of the title can be capitalized as “20 Foolproof and Completely Essential Job Interview Tips.”