People hate prepositions. Just mention the word to a classroom of kids, and you have the chance of hearing everything from groans to screams, sighs of sadness, even a sarcastic laugh or two. I can understand why--the word "preposition" is scary and unfamiliar. We never learn prepositions the way we learn nouns or adjectives. There are no "preposition" blanks in Mad Libs.
Just relax. Prepositions are really quite easy. Let's start by re-hearing, or re-interpreting the word. That is, stop pronouncing it "prep-o-sition," and say instead "pre-position." You hear that hidden word, position? That's the key to understanding. A preposition is a word that indicates the position of something...no more, no less.
So, what is the coffee's position in relation to the mug? Unless there has been some scalding accident, the coffee is probably IN the mug. How about butter's relationship to toast? That's right, the butter is ON the toast. Birds are IN trees, dogs are ON porches, and bees are, hopefully, ABOVE me in their hive, not landing ON me.
These tangible or physical positions are easy to see, and therefore easy to grasp. In fact, Dr. Seuss was the king of the preposition, and should be required reading in grammar class--everyone knows The Cat in the Hat. But what about the more intangible uses of prepositions? Well, here is where we get into the land of metaphor.
What, exactly, does it look like to be "under the weather?" Do you see a runny nose, or a person with a raincloud hanging over her head? For that matter, how about that big decision or credit card debt hanging "over" you? Lots of us know what that feels like. But because sickness, debt and decisions are not physical things, prepositions help to make them more understandable--sometimes even easier to deal with. I don't know about you, but I'd rather picture my debt as a big, cartoon anvil levitating above me than the very real monetary amount. Perhaps, like Wile E. Coyote, I'll bounce right back when it inevitably falls ON my head.