3.2: Past Modals of Degrees of Certainty
- Page ID
- 275450
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Degrees of Certainty – Past
CERTAIN – REFLECTION
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Verbs in the past tense or past perfect express fact based on known information or details. However, past modals may (not) have; might (not) have; could (not) have and must (not) express varying degrees of uncertainty. They are opinions based on inference, putting together known details and coming to a conclusion. |
COMPARE VERB TENSES AND PAST MODAL |
| AFFIRMATIVE |
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Polar ice melted. Polar bears lost their icy habitat. Polar bears must have lost their food supply. |
NEGATIVE |
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Polar bear cubs didn't die from the cold. Polar bears could not have fed their cubs. (Very low possibility-considered impossible) |
CLAUSE |
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I am (was) sure that polar bear cubs died from starvation. It is (was) likely that polar bears found no food for their cubs. |
UNCERTAIN – SPECULATION |
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Past modals might have and could have express opinion based on very little information, a guess (with perhaps other interpretations) or speculation about a past situation. |
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MODAL |
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Polar bears may have found other food sources. Polar bears might have found other food sources. Polar bears could have found other food sources. |
NEGATIVE MODAL |
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Polar bears may not have found food for their cubs. Polar bears might not have found food for their cubs. |
CLAUSE |
It is/was doubtful that the polar bears found any ice from which to hunt seals. |
reflection (N) – remembering the past
inference (N) – something that you think is true, based on information that you have
speculation (N) – a good guess; likely
Also see Might / Must have – past guesses and inferences
Must
One word with two meanings.
Must (inference) vs. Must (necessity)
#1 MUST |
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A speaker uses must to express a logical conclusion, an inference based on clues or information that one knows. The speaker's certainty is "strong". |
AN INFERENCE / A CONCLUSION |
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Polar bears go into seaside towns looking for garbage. |
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Ice no longer covers the polar regions all year. |
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A normally peaceful bear attacked and killed some arctic campers. The bear must have been looking for food. (near certain) |
#2 MUST |
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A speaker also uses must to express obligation, duty, or necessity, something that someone "has to do". The speaker's opinion is "strong". |
NECESSITY / OBLIGATION |
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Polar bears must be fed or relocated. (strong – necessity) |
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Polar bears must swim long distances to find ice and seals to eat. (strong – necessity) |
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The campers had to shoot the bear. |
Exercise 1: Rewrite the Sentence-Past Modals
Rewrite the sentences with the choices given.
Example: Perhaps she jumped
A. may have
B. could have, could've
Answer
A. She may have jumped. B. She could have jumped.
1. Maybe he said that. She can't remember now.
A. might have
B. could have
A. ___________________________ B. ___________________________
2. Perhaps she saw us.
A. could have
B. might have
A. ___________________________ B. ___________________________
3. I'm pretty sure we took the wrong street.
A. must have
A. ___________________________
4. It is not possible to have happened.
A. couldn't have
A. ___________________________
5. I wish you had seen it. It was spectacular!
A. should have
A. ___________________________
6. It is possible to have happened but not likely.
A. could have
A. ___________________________
8. It was possible for him to go but he didn't.
A. could have
A. ___________________________
inference (N) – something that you think is true, based on information that you have
See Should /Must and Must / Must have.
Also see Modal Review – Obligation.