auxiliary verb should

1. used in the first person to indicate simple future time I shall probably go tomorrow
2. used in the second or third person, esp. in formal speech or writing, to express determination, compulsion, obligation, or necessity you shall listen
3. used in the statement of laws or regulations the fine shall not exceed $200
4. used in questions about what to do shall I invite them?
5. used in formal conditional subordinate clauses if any man shall hear, let him remember

Etymology: ME schal, pl. schullen < OE sceal, inf. sceolan, akin to Ger sollen < IE base *(s)kel-, to be indebted > Lith skeliù, to owe