I am going to imply that I have a feeling which doesn’t let me believe something can be absolutely true (I have some doubts in my mind whether it is true or still I should not believe it completely.) How can I convey this message?
I know two idioms:
First: Deep down inside
Second: in one’s stomach (I have just heard this one, but cannot find any reliable source for it.)
Let me make up a scenario to clarify my intention.
I am wondering which one of these two idioms can be used in scenario below?
Though he told me that he would pay me back the money he borrowed three months ago, but………..
a. deep down inside, I don’t trust him. Because I know that he’s unemployed at the moment.
b. I don’t trust him in my stomach. Because I know that he’s unemployed at the moment.
To me, ‘a’ makes a perfect sense, but I doubt if it is natural here.
I have never heard “in my stomach.” I suspect what is intended “in my gut.” What is meant by that informal figure of speech is a belief held either without any objective supporting evidence or despite objective rebutting evidence. So it is not completely appropriate in the scenario that you sketched because you have objective evidence making his payment doubtful, namely his being unemployed.
The “deep down inside” figure of speech has a very similar meaning but tends to be limited to beliefs about emotional states, which by their very nature cannot be supported by objective evidence.
He says he loves me, but deep down inside, he is still in love with his former wife.
So again it is not totally appropriate in your scenario.
But there are lots of ways of informally expressing doubt ranging from the mild disbelief of
I have my doubts
to the utter incredulity of
Yeah, when pigs can fly
I am not saying that “in my gut” and “deep down inside” are not common. They are quite common ways to preface an opinion that can be backed with little or no evidence. But neither seems quite right for the type of situation that you have specified.