Anybody can interpret what the difference is among “when, where, should”? The example sentence I find is: A tenant may be liable to his landlord should a fire cause damage to the premises he rents. I think “should” can be replaced by "when or where". Can you tell me the rules or reason why? If possible, please give me a few examples to distinguish the three. Thanks.
It is not being used as a synonym for "when or where," it is closer to being a synonym for "if." In this usage, should creates a conditional statement. If there is a fire, then the tenant may be liable for the damage.
The relevant definition from the Oxford English Dictionary with some examples:
Shall/Should Definition 19 c. In the apodosis of a hypothetical proposition (expressed or implied), indicating that the supposition, and therefore its consequence, is unreal. Where the future tense (or the present with future import) would be used if the supposition were entertained. (With past tense subjunctive, usually should or would, also could, might, arch. were, etc., in the apodosis. Cf. 21) Now somewhat rare, modern usage preferring were to.
Ex. 1884: Tennyson Becket iii. i. 120 And no flower, not The sun himself, should he be changed to one, Could shine away the darkness of that gap.
Ex. 1782: F. Burney Cecilia V. ix. iv. 81 Should I think, Sir, to eternity,..I could never conjecture what you mean!