should

modal verb: used to give advice or express what is considered right or sensible
- You should back up your files regularly.
modal verb: used to indicate expectation or probability
- The package should arrive tomorrow.
modal verb: used in questions to make polite suggestions or ask for advice
- Should we start the presentation now?
modal verb: used with ‘have’ + past participle to express that something was expected or advisable in the past but did not happen
- I should have saved the document before closing it.