Prepositions: ON vs. OFF (Obama vs. Taylor Swift)

The meaning of prepositions often puzzles learners of English. However, it is one of the things I like about english grammar. Over the years, I have come to the conclusion that prepositions in English, compared with Spanish, are wonderful.

Why? Because they make sense. Prepositions in Spanish often have a vague meaning or they are too flexible. However in English they have coherent meanings that are rarely contradicted. To put it in rules:

a) A preposition in English always (every rule has its exceptions) has the same meaning.
b) that basic meaning can be elaborated on, but it will remain basically the same.
c) as a consequence with a little common sense, the meaning of prepositions can be predicted... and so can phrasal verbs.

So, what is the meaning of ON and OFF? These two prepositions which are clearly opposites, are often misunderstood by many students and approached incorrectly by too many teachers. Any possible meaning of on falls within the category of "in contact". Any possible meaning of off can be reduced to "no contact".

Both meanings have to be interpreted broadly. But the basic meaning remains. Let's take the expression "that's on me" which apparently makes no sense. Where is the contact here? The contact here is the connection  between the person who says that sentence and the payment to be made.

"That's on us, not on them."

Here, Obama is using it even more metaphorically: he is discussing Obamacare and its failings and he is taking the blame, as if it were the bill at a bar. So, he can still use "That's on us." Even here, on means contact, in the sense of belonging which is a type of connection.

Now to off. Recently american singer Taylor Swift provided us with a very good example of using "off" in a metaphorical way, actually a phrasal verb (phrasal verbs are more or less elaborated metaphores).

The name of the song is shake it off. If you think about it this phrasal verb is ingenious and straightforward at the same time: the message is to stop worrying about stupid problems which are really unimportant. This is something that happens a lot when you are a teenager. The idea of separation is there, separating from those problems. This is a metaphorical turn on the original use of shake off, which is what you do with snow, dirt, dust, etc... when they accumulate on your clothes.

A good exercise would be to take any sentence you can think of that includes on or off and figure out how these prepositions retain the original meanings. If you can't figure it out, you are welcome to post it as a comment!