must/should have done

[norwolf]

Hi teachers:
We say: It must have been Tom that parked the car here, as he is the only one with a car.

Can we replace "must" with "should"?
---It should have been Tom that parked the car here, as he is the only one with a car.


Thank you in advance.

[wmuench]

I believe yes you can in this instance if the rest of the text is written in the same style. It's more commonly used in Britain.

Please read (in particular) the last paragraph under usage.

"Should"

–auxiliary verb 1. pt. of shall. 2. (used to express condition): Were he to arrive, I should be pleased. 3. must; ought (used to indicate duty, propriety, or expediency): You should not do that. 4. would (used to make a statement less direct or blunt): I should think you would apologize.

Origin:
ME sholde, OE sc(e)olde; see shall.

Synonyms:
3. See must 1 .


Usage note:
Rules similar to those for choosing between shall and will have long been advanced for should and would, but again the rules have had little effect on usage. In most constructions, would is the auxiliary chosen regardless of the person of the subject: "If our allies would support the move, we would abandon any claim to sovereignty. You would be surprised at the complexity of the directions."

Because the main function of should in modern American English is to express duty, necessity, etc. (You should get your flu shot before winter comes), its use for other purposes, as to form a subjunctive, can produce ambiguity, at least initially: "I should get my flu shot if I were you."

Furthermore, 'should' seems an affectation to many Americans when used in certain constructions quite common in British English: "Had I been informed, I should (American would) have called immediately."

"I should (American would) really prefer a different arrangement." As with shall and will, most educated native speakers of American English do not follow the textbook rule in making a choice between should and would.

[bhaisahab]

Hi teachers:
We say: It must have been Tom that parked the car here, as he is the only one with a car.

Can we replace "must" with "should"?
---It should have been Tom that parked the car here, as he is the only one with a car.


Thank you in advance.

No you can't use 'should' in this context it is not at all idiomatic and it doesn't have the same signification.