Modals of deduction and speculation

In this blog entry we begin our discussion on grammar from the Fortune Gold series focusing firstly on modals of deduction and speculation.

We use modal verbs to deduce and speculate about something. The modals for this are: could, may, might and must.

The basic form is modal + base form verb. For example – He might leave.


The choice of modal (e.g. must vs. could) shows how confident we are that our guess is correct.
Must                     =            High certainty
May                      =            Some certainty
Might / Could   =            Low certainty

For example:
• “How old do you think Mrs. Jenkins is?” “Well, her son is at university so she must be at least 40.”
The speaker is guessing but confident about the guess.
• “What’s the weather like in Abu Dhabi?” “Well, it’s summer now, so it could be over 40°C/104°F this week.”
The speaker is less sure about her guess.


We use a modal + base form to deduce or speculate about a possible (present) state or current habit. For example: They speak Spanish so they could be from Chile.
• Here, we notice something (They speak Spanish) and we try to explain it (they could be
from Chile).
• Similarly: Jerry is very tall so he might be good at basketball.
We use a modal + have + past participle (-ed or –en form) to deduce or speculate about a possible past event or state. For example: I can’t see Julie anywhere. She might have finished her homework early and left.
• Here, we notice something in the present (Julie isn’t here now) and we try to explain it with a past event/state (Julie finishing her homework early).
• Similarly: My stomach hurts. I may have eaten too much.

If you are interested in learning more about modals of deduction and speculation, don’t forget to follow our grammar video lessons: