We often speculate, or make “best guesses”, about past situations based on facts that we have. The modal that we choose depends on how certain we are about our speculation. affirmative; Must have, Had to have, May have, Might have, Could have Negative; Can’t have, Couldn’t have, Must not have, May not have, Might not have When you are almost 100 percent certain that something was possible, use must have or had to have. The statues are very big. Speculation· They must have been hard to move. When you are less certain, use may have, might have, or could have. The islanders were able to carve the stone. Speculation; The stone may have been quite soft. When you are almost 100 percent certain that something was impossible, use can’t have or couldn’t have; The islanders couldn’t have moved the stone! It was too heavy. When you are slightly less certain, use must not; They must not have moved it without help. Use may not have or might not have when you are less certain. The islanders might not have moved the statues over land. They could have used boats. There is a man badly injured in the hospital. Complete what his friends are saying about him, using each of these verb forms. couldn’t, may have, may not, could, may, might have

It means: guessing. Are you referring to "might" and "will"?