Usage of "alone" (Bob alone can help you.)

[Yeongheon]

Hi,

I would like to know why sentence (b) is ungrammatical while sentence (a) is grammatical.

(a) Bob alone can help you.
(b) *Call Bob alone.

I would be grateful if anyone could help me out.
Thank you in advance!

Yeongheon from Daegu, South Korea

[Yankee]

Hi Yeongheon

(a) Bob alone can help you. ==> The sentence means "Only Bob can help you".

(b) *Call Bob alone. ==> This sentence is unclear. It seems to be trying to say "Call Bob when you are alone."
.

[Yeongheon]

Thanks, Amy!

As a future English teacher, I want to make sure that I can explain things clearly about the English language.
Once again, I thank you for your kind help. And I like your smile in the photo. ^^

Yeongheon

[Sweetpumpkin]

Hi, Yoengheon. Your question reminds me of a question in the official appointment exam(imyonggosi in Korean) for English teachers. I don't have the answer, but it seems to be a very interesting question. I can't wait the answer coming.