MODALS of DEDUCTION

 

PRESENT & PAST

PRESENT

 

We use modal verbs to say how sure we are about something.

 

 

1. MUST

 

We use MUST when we feel sure that something is true because there's a very strong evidence.

 

• He must live near here because he comes to work on foot. (We don't know where he lives but we're sure it's not far away)
• Come inside and get warm - you must be freezing out there.

 

Notice that MUST is followed by an infinitive without "to".

 

 

 

2. MIGHT, MAY, COULD

 

We use MIGHT, MAY, COULD to say that we think something is possible but we're not sure.

 

• Did you hear that? I think there might be a burglar downstairs. (We're not sure there's a burglar but we think it's possible)
• We'll try to get there early but we may arrive late if there's a lot of traffic.

 

Notice that MIGHT, MAY. COULD are followed by an infinitive without "to".

3. CAN'T

 

We use CAN'T when we feel sure something is not true.

 

• It can't be a burglar. All the doors and windows are locked. (We don't know it's not a burglar but we feel sure it's not)
• It can't be far away now. We've been driving for hours. Where's the map?

 

Like the other verbs CAN'T is followed by an infinitive without "to".

 

 

*Remember that all of these modal verbs - must, might, may, could and can't have other uses.

PAST

In the same way that we use modal verbs to say how certain we are about things in the present we can also use them to speculate about the past. 

 

Have + past participle is called the perfect infinitive. When we use modal verbs to talk about the present they are followed by an infinitive without "to". When we use modal verbs to talk about the past they are followed by a perfect infinitive.

1. MUST + PERFECT INFINITIVE

 

We use must + perfect infinitive when we feel sure about something in the past.

 

• You must have been delighted when you heard you'd won the lottery.
• The thieves must have come into through the window. Look - it's still open.

 

 

2. MIGHT, MAY, COULD + PERFECT INFINITIVE

 

We use might, may, could + the perfect infinitive to say that something was possible in the past but we're not sure.

 

• The thieves might have escaped by car but we are not sure.
• I can't find my purse. I could have left it in the supermarket but I just don't know.

 

3. CAN'T + PERFECT INFINITIVE

 

We use can't + the perfect infinitive when we feel sure something didn't happen in the past.

 

• I thought I saw John in town this morning but it can't have been him - he's in Greece this week.
• I can't have left it in the supermarket -  I had it on the bus on my way home