What is a good mnemonic rule that an English learner can use to remember the difference between its (possessive adjective: a team has started its lunch) and it's (verb: it's raining)?
I'm not sure of how good a mnemonic this is, but it's always worked for me. When proofreading, I simply remind myself:
So, when I say:
I recognize that "It's" means "It is", so I leave the apostrophe in. But when I type and proofread:
I realize that "it's" does not mean "it is"; it means "the foundation belonging to it", so I remove the apostrophe:
If you don't like my method, it's easy to find lots more on the subject.
You just know that it's stands for it is, two words.
When reading, you just see if it is a single word or two words "linked" with an apostrophe.
For writing, you may employ this mnemonic:
A tear will resemble to write it with an apostrophe.
Its and my is "just one word".
If I can substitute its (one word) with another possessive adjective my (one word), and the resulting phrase is grammatical then there is no need for the apostrophe e.g.,
"my lunch" is grammatical so no apostrophe is required (the possessive adjective, its, is 'just one word'.)
When we substitute it's raining (or its) with my we get:
"My raining" as a phrase is not grammatical so it's is the correct spelling (two words; it + is)
Further examples: (thinking 'yes' or 'no' for grammatical and ungrammatical)
The company has lost my licence ----> grammatical ---> my ('just one word') ---> its
Check to see if my gone ----> ungrammatical ---> we need two words ---> it's (it + has)
... chases my prey through the coral ----> grammatical ---> my ('just one word') ---> its
This isn't my book, my Fernando's. ----> ungrammatical ---> we need two words ---> It's (It + is)
The dog is eating my dinner ----> grammatical ---> my ('just one word') ---> its