One of the most famous fake grammar rules is the one about not allowing prepositions at the end of sentences (terminal prepositions). 'Preposition' is a grammar word labelling a word (or group of words) used to show the place, time or direction of a noun. Usually prepositions appear before the word they describe.
Examples with the preposition in bold:
The cup is on the table.
The chicken is in the congee.
The boat is far from shore.
The plane flew towards Guangxi.
The full form of this fake rule is that: Prepositions should only appear before the word they relate to and never at the end of a clause or sentence. The rule is included in (poor quality) textbooks, but commonly ignored outside the classroom.
The problem started with John Dryden in the 17th century. He believed that Latin was better than English and that English should be reformed to be more like Latin. In his defence Dryden lived at the time that English was changing into its modern form. When Latin and English had a different structure Dryden suggested that the Latin way of speaking was better. In Latin grammar, sentences do not end with prepositions.
For generations English grammar teachers have been trying to force us to do as Dryden suggested. They failed; English speakers still sometimes end sentences with prepositions. The main reason that they failed is because some English structures can use or even require a preposition at the end of a clause or sentence. These include wh-word clauses, relative clauses, passive voice and exclamatory sentences.
What are you looking at?
Look at where the boy came from.
It is not a car you could depend on.
I like the house that Tom is next to.
That was what I was thinking of.
The car has not even been paid for.
You must feed your pet enough to live on.
She didn't have any help worth speaking of.
Look at the trouble you have got us in!
Don't push, you are next!
Trying to reword these sentences to follow the fake rule can produce awkward results. There is a story that Winston Churchill once demonstrated this problem by saying, "This is the sort of English up with which I will not put."
There is one slang structure that needs to be pointed out. Adding an extra preposition at the end of a sentence is wrong. For example: Where are you at? is better written as Where are you?If a preposition can be cut off the end of a sentence, without changing the meaning, remove the preposition.
Usually a preposition is placed before the word it refers to. However some sentences and clauses require it to be placed at the end. The desire to change English and make it look more like Latin is useless in the modern world. Old books, famous authors and modern publishers all ignore this fake rule. Rewording sentences to fit a fake rule is difficult and results in poor English. Trying to teach it is more of a parody than an English lesson.