In German, when we want to express a supposition we can use modal verbs (Modalverben). Depending on the modal verb, the strength of the supposition (how likely it is to happen) can be adjusted. Today's article introduces the subjunctive of supposition with modal verbs.

Let's get started!!!

1. Können 

• Normally the verb können is used to express possibility or opportunity. When you want to express a conjecture with a very low likelihood, you can use the Konjunktiv II of können, which is könnten.

Es könnte sein, dass es heute noch regnet.

(It could still rain today.)

• When you want to make a slightly stronger prediction, use können. 

Es kann sein, dass es heute noch regnet.

(It may still rain today.)

!!! Note: When kein or nicht is added, the supposition with können CANNOT happen.

Es kann heute nicht regnen.

(It cannot rain today.)

2. Dürfen

• When you want to express a conjecture stronger than könnten and können, use dürfen in Konjunktiv II, which is dürften. 

Es dürfte heute noch regnen.

(It will probably rain today.)

      → The likelihood of rain is relatively high.

3. Müssen

• A supposition with müssten (Konjunktiv II) is stronger than dürften; the likelihood is high. 

Es müsste heute noch regnen.

(It must be going to rain today.)

• A supposition with müssen is very strong; the action or event will certainly happen.

Er muss heute zum Arzt.

(He has to go to the doctor today.)

      → He will definitely go to see the doctor today. 

!!! A supposition with können can be used like müssen when nur is added: 

Das kann nur meine Freundin wissen! 

= Das muss meine Freundin wissen!

(My girlfriend surely knows this.)

4. Sollen

• The modal verb sollen can be used when you want to express an expectation that something will happen.

Nach der Wettervorhersage soll es heute noch regnen.

(According to the weather forecast, it is supposed to rain today.)

      → Using sollen in this case, the speaker predicts that it will rain but needs additional information as a basis for the conjecture.

• The speaker also expresses an expectation about an action or event that often happens, with sollten. You can add eigentlich to increase the degree of accuracy.

Es sollte (eigentlich) heute noch regnen.

(It is (actually) supposed to rain today.)

5. Mögen

• The verb mögen concedes that a certain action or event is actually taking place. In a supposition sentence with mögen you can add ja or schon to confirm that the supposition is true.

Es mag (ja) sein, dass es heute noch regnet, aber ich brauche keinen Regen.

(It may be raining today, but I don't need rain.)

     → It is already raining.

Es mag (schon) sein, dass du recht hast, aber ich habe trotzdem Zweifel.

(You may be right, but I still have my doubts.)

     → You were right. 

*** In addition, when you want to express a conjecture you can use adverbs with an equivalent meaning.

Er muss zu Hause sein.

= Er ist ganz sicher zu Hause.

(He is certainly at home.)

In summary: