What are you on about now? (Prepositions: on vs about)

When something has a topic, is it ON that topic, or ABOUT that topic? This question on, or about, which preposition to use comes up fairly often.  Martha’s answer tries to explain some of the connotations that may be present when using certain words.

• A discussion about a topic — this implies that the discussion was just a conversation, really, and it might not have stayed strictly on-topic.
• A discussion of a topic — this brings to mind a true discussion, going into all sorts of details of the topic (and only the topic).
• A discussion on a topic — here I picture the discussion to be somewhat one-sided, almost a lecture.

I’m afraid to say that I don’t agree with these explanations.  My instinct is that “about” and “on” are pretty much equivalent in meaning, as FumbleFingers wrote.

But if there are two words, and they both serve a similar purpose, which should we choose? People must care about this, because they keep asking.  It turns out that EL&U is not the only place people have asked. A blog post on twopens.com asked the Chicago Manual of Style editors which was better:

She gave a lecture on recycled plastics or about recycled plastics.

A lengthy discussion ensued until one editor pointed out that it didn’t matter at all, since the meaning was perfectly clear and concise.

Until, of course, you have a sentence like

I once attended a lecture on the surface of Mars. (How did you get there?)

Now we have a pickle. The word “on” has many definitions, so once your sentence invokes one of those other definitions you risk confusing your reader. If you’re careful, you can spot the double meanings and edit your sentence accordingly. Or, you can be cautious and just choose “about” which has less potential for error.

Finally, if you want to just go with the flow, you can simply do whatever everyone else is doing. If you can figure out what that is, of course.

Ratio of On to About

(Ratio of less than one means About is used more)

*Note: Many false positives here, such as: “found the book on Amazon.com”, “book on tape”, etc.

From my crude Corpus search, it seems that there is no clear winner in usage. The numbers for “on” are inflated by the fact that many examples are false positives, yet there still is an overwhelming usage of “on” for certain phrases. So don’t get too hung up about about, or go on and on about on. It’s all okay.