12-1 Past Probability

Modal Verbs

• can
• could
• may
• might
• shall
• should
• will
• would
• must
• ought to

• They do not change forms like other verbs.
  • go, goes, went, gone / look, looks, looked, looked

• There is no do / does in the question forms.
  • Can you give me a hand, doctor?

• There is no don't / doesn't in the negative forms.
  • The pharmacy shouldn't do that.

• They are always followed by a base form verb.  "Ought to" (rare) is the only exception as it takes "to" or "not to" before the verb.
  • We would help more patients if we had time.
  • Dr. Badger mustn't do that!
  • That technician ought to get going. (rare = should is more common)

• They do not usually have past or gerund forms.  Other verbs are used instead.
  • I hate having to draw blood. (must)
  • I was able to listen better before I began to go deaf. (can)

• Some modals are used with the Perfect Infinitive to make past forms.  This is explained more below.
  • The doctor shouldn't have done that.
  • Dr. Ray must have stayed home.

Modal Verbs of Probability in the Past