1. your sister is going to do you a favor by picking them up 2. you are forcing your sister to pick them up 3. you are basically asking your sister to pick them up, but not kindly 4. you are politely requesting your sister to pick them up for you 5. like 2, you are forcing your sister to pick them up
Depending on the circumstances, I'll let her do it would be completely fine. "The photos will be ready about 10, and my sister said she had to go to the store tomorrow morning - I'll let her pick up the photos for me."
Using TELL in the context of telling someone to do something says you that you have the authority over that
So, "I'll let my sister call you when she comes home" and "I'll have my sister call you when she comes home" mean the same thing? (My sister is not home.)
I wonder if "let sb. do sth." is always equivalent to "have sb. do sth." or it all depends on the context?
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I looked up a dictionary. 'Tell' has a meaning, which is close to "SAY" --- expres
I suggest leaving "let" out of the mix. It means "allow" or "grant permission" and you can find other words to say what you mean besides "let" if you find its use at all confusing, and it's certainly understandable how you could. In the telephone example, it's safer to say "I'll tell (say to) my sister that you called. But you could also say "I'll let her know" - which I guess means "I'll allow h