Modals

POSSIBILITY PROBABLITY NECESSITY ABILITY

Pres: can should must can could would might must

(theoretical) -------------------------------------------------------------------------------------- may could might

(factual) --------------------------------------------------------------------------------------

Past: could have should have _________ could may have must have --------------------------------------------------------------------------------------

Past

Unfulfilled: could have _________ _________ (could have) might have --------------------------------------------------------------------------------------

PERMISSION OBLIGATION WILLINGNESS SUGGESTION

Pres: can should will* could may shall* might would should --------------------------------------------------------------------------------------

Past: could ________ would have ________ --------------------------------------------------------------------------------------

Past

Unfulfilled: could have should have (would have) could have should have --------------------------------------------------------------------------------------

*Traditionaly, will was reserved for promises, while shall was used for any other expression of future willingness; however this distinction has nearly disappeared from the language, with will becoming the popular form for all expressions of future.