Past modals

Dear teachers,

I would lile to ask you some big questions, and please be any help.

I read in my text book about the use of past modals for degrees of certainty and opinions and advice.

For degress of certainty, the book says:

• Probability:
  • She must have left already.
  • She must not have wanted to come.
  • She couldn't have forgotten the party.
• Possibility:
  • She may have forgotten our invitation.
  • She might have forgotten the time.
  • Her car could have broken down.
  • She may not have wanted to come.
  • She might have remembered the time.
• My questions:
  • What is the difference between probability and possibility?
  • Why "must" and "could" are for probability but "may", "might", "could" are for possibilty?
  • Does the past modals uesd here mean something happened in the past? If it is true, then why can "may" be used here since it is a present modal?
  • Can we consider all the sentences above to be conditoinal sentences because they all look like in past perfect tense here?

For opinions and advice:

• He could have left earlier.
• He shouldn't have stayed so late.
• I would have asked him to leave.
• I wouldn't have stayed so late.
• He could have been more considerate.
• You could have reminded him of the time.
• My questions:
  • These sentences seem to be more like conditional sentences. Something did not come true but someone dreamed about it. Right?
  • These sentences (opinions and advice) are a lot similar to the former ones (degrees of certainty), how do we tell them apart, or do they mean the same to you?
  • Why there is no "may" to be used here?

Thank you for your time and I am sincerely looking forward to your advice.

LCChang

This doesn't directly address your questions, but it might be helpful nonetheless. http://en.wikipedia.org/wiki/Modal_logic

Hmm, it works fine for me. Did you try copying the link and pasting it into the "navigation bar" of your internet browser?

Lcchang wrote:

Can any teacher help, please?

Hello Chang

I guess you are asking rather the semantic difference(s) between "possible" and "probable". Right? I found a good site online to explain this. Here they say like below.

Christianlogic.com wrote:

Difference between Possible and Probable All of us can confuse these important ideas: (1) what is impossible, (2) what is possible, and (3) what is probable. Let’s explain the difference. (1). Something is "impossible" if there is no way that it could be true. (EX) Jack realized he'd made a revolutionary discovery. When you add two plus three underwater, you always come up with seven. Every math textbook must be rewritten! (2). Something is "possible" if there is a chance that it could be true. (EX) Little Girl said "Mom, is it possible the hospital switched me at birth and I'm really a princess?" Mother answered, "Yes, but it’s not likely. Now eat your asparagus – even a princess must eat her asparagus." (3). Something is "probable" if it is more likely true than not true. We must weigh the evidence and decide. (EX) An annoyed dairy farmer said, "Dulcy(=a cow) got out of her pen again, and I can't find her - she's probably on the other side of the moon". His calm wife answered, "No, she always goes for my strawberries - that's where you'll probably find her." If someone chooses to believe a "possibility" while ignoring evidence that supports an obvious "probability", he is using the "possibility" fallacy. Our cure for this fallacy is to look at the evidence as if we were holding a balance scale. We look at the evidence, and we filter out the possibilities that are probably not true. This is hard for people like us! We never want to throw away our favorite possibilities. But we need to get this right; so many choices in life can depend on judgments like this. [Exercises] In the examples below, indicate whether what is said is (1) totally impossible, (2) possibly true, or (3) probably true. No evidence is given; simply use your knowledge of history, science, or the Bible. 1. Moses and King David were great friends. They often went out for a milk shake at Checker's drive-in. 2. Abraham Lincoln decided to grow a beard after a little girl wrote him a letter saying he'd look better with one. 3. The tallest mountain in the lower forty-eight states is west of the Mississippi. 4. An Iowa farm boy said, "Mom! Dad was out plowing the cornfield, and the tractor almost fell in a new volcano that's forming out there! Call the fire department!" 5. NASA’s Opportunity rover has found evidence of water on Mars. 6. Home Schooling Today magazine is actually a covert CIA operation used to send coded messages to agents in Argentina. 7. Honeybees never sting when they're foraging for nectar. 8. Grandpa, with four-year-old grandson on his knee: "When I was your age, I did mountain climbing. I remember the day I summited on Everest alone. . . ." 9. Read the following example and choose whether A or B is the wiser choice based on the evidence in the story. Advertisement: "Invest in our lead teacups - this is how the super-rich protect their wealth! We know the price of lead teacups hasn't changed for two hundred years, but this is only a trick. We've studied the market, and we have secret information that the price of lead teacups will soon go through the roof!" A: I should invest because it is possible lead teacups will increase in value. B: I should not invest because lead teacups will probably not increase in value. [Answers] 1. Impossible. The Bible says Moses was dead before King David was born. 2. Probably true. 3. Probably true. 4. Possible. It's always possible a new mountain will form in Iowa. 5. Probably true. NASA is a reputable institution. 6. Possible. 7. Nathaniel: "Probably true." Hans: "Impossible. I've been stung in the eye by one of Nathan's bees when I wasn't near the hives." 8. Impossible. It is not reasonable that a four-year-old could climb Mount Everest alone. 9.  B. If the price of lead teacups hasn't changed for the past two hundred years, it's not likely it will today.

Paco's conclusion: If you can deny something with some evidence, it's impossible. Otherwise you can say it's possibly true. If you have any kind of evidence to support the possibility, you can say it is probable whatever the probability might be.

paco

Modals are auxiliary verbs to express in what way or how the speaker thinks NOW about some event.

(1) When the event is the one that is happening now or in future, you use the form <modal+V>.  
(EX) Mr. Chang speaks good English. He must study English hard now.
        He must study English hard now. 
        = I think it is highly probable that he studies English hard now.

(2) When the event is the one that happened in the past, you use the form <modal+have+V-ed>. 
(EX) Mr. Chang speaks good English. He must have studied English hard in the past.
         He must have studied English hard in the past.
         = I think it is highly probable that he studied/(has studied) English hard in the past.

paco