Under modern constitutional conventions, the sovereign acts on the advice of his or her ministers. Since these ministers most often maintain the support of parliament and are the ones who obtain the passage of bills, it is highly improbable that they would advise the sovereign to withhold assent. An exception is sometimes stated to be if bills are not passed in good faith, though it is difficult to make an interpretation on what this circumstance might constitute. Hence, in modern practice, royal assent is always granted; a refusal to do so would be appropriate only in an emergency requiring the use of the monarch's reserve powers.
Is it probable, improbable, or impossible that a sovereign would withhold assent?
improbable