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should

should /ˈʃʊd/ /ʃəd/ verb
should
/ˈʃʊd/ /ʃəd/
verb
Britannica Dictionary definition of SHOULD
past tense of shall
[modal verb]
used to say or suggest that something is the proper, reasonable, or best thing to do
used with have to say that something was the proper, reasonable, or best thing to do but was not done
used with have to say that you wish someone had seen, heard, or experienced something
used to ask for someone's opinion
used to say that something is expected or correct
used when saying that you feel a specified way about someone's words or behavior
used to emphasize what you believe, think, hope, etc.
used with have in negative statements as a polite way of thanking someone for doing something
somewhat formal used to talk about the result or effect of something that may happen or be true
usually used with if
British used to say that you would do or feel something if something specified happened only used after I or we
British used when giving someone advice only used after I or we
British used to say that you want to do or want to have something only used after I or we

how/why should I/we know

used to say that you do not know the answer to a question and are surprised that you were asked it

what/who should you see but

used to say that you are surprised to see something or someone