TITLE: Difference between a proposition and an assertion
QUESTION [5 upvotes]: It may be a silly doubt, but let me ask this.

What is the difference between a proposition and an assertion?

I know there's a very thin line between  the two terminologies, but I'm unable to get that.

REPLY [4 votes]: An assertion is a proposition that is claimed to be true.
Proposition P1:  The tree is tall
(This might be true or might be false, and it can be just an idea proposed for consideration, apart from anyone's actual beliefs. It may be thought or expressed.)
Assertion A:  "The tree is tall."
(This might be true or might be false, but it is a statement of a proposition claimed to be true. Generally, someone purports to believe it and offers it as fact.)
The assertion is itself equivalent to a proposition (P2) about proposition P1:
A = P2:  P1 is true.                                              (P2 is the assertion of P1.)