Today’s Good Word, predator, contains the following line: “. . . adults who try to seduce our children on line.”
Paul Ogden, one of the daily Good Word editors, commented that the spelling online 1.7 billion hits on Google (that’s right—billion) while on line gets a mere 450 million.
My view is that on line is a slightly idiomatic prepositional phrase (PP) while online and on-line are forced adjectives from the PP. In the phrase above, “children on line” (as opposed to “online store”) we need a PP rather than an adjective, which would imply some quality the children have.
To test my sentiment, Paul searched “I am online” and “I am on line” and “I am on-line” and came up with these results: “I am on line” or “I am on-line” gets 38,000 Google hits. “I am online” gets 444,000, indicating the flow of this issue is not following my sentiments.
This issue is part of a broader one on which I wrote while still an academician with time to research it in greater depth. English is a very odd language in that it allows PPs to be converted into adjectives. Over-the-counter drugs, off-the-shoulder dress, around-the-world cruise, on-line activities are all accepted slang conversions of PPs into adjectives. We know that they are adjectives because PPs in English always follow and never precede the noun they modify while adjectives behave in just the opposite manner.
Now, I am not a prescriptive grammarian; grammar should be flexible and change over time. However, it always changes in a consistent, rule-governed manner. Moreover, the very purpose of grammar, the set of rules which governs the way we speak, is to provide consistencies that we can depend on in the interpretation of what we say and hear. In this case, “I am on line now” and “I use an on-line store” would be consistent with all the other PP adjectives out there.
I said that these hyphenated adjectives are slang even though all the examples I cited seem perfectly normal, often used in fairly formal contexts. This is explained by the difference between “grammatical” and “acceptable”. Words like stick-to-it-iveness, one-ups-manship—even talkative with its Germanic stem and Latin suffixes—are all ungrammatical in that they are inconsistent with the rules of English grammar. However, they have been accepted because they are either amusing or useful.
There are lots of idiomatic exclusions and maybe online has become a ‘stick-to-it-iveness’ adjective already. The PP on line is itself slightly idiomatic since it cannot be used with the or a, so maybe nothing is at stake here. However, so long as the point of grammar is consistency in speech, the consistent way to handle on line is without a hyphen when it is clearly functioning as a PP and with a hyphen when it is functioning as an adjective in attributive (prenominal) position. The form with neither a space nor hyphen is probably the result of our adjusting to URLs that generally ignore them.