1. The verb suppose can have two meanings in the kind of passive sentences where it is followed by an infinitive:
   
   
   1.- An ordinary passive sentence, with the same meaning as an equivalent active sentence:
   
   
   People suppose he is in Paris.
   
   He is supposed to be in Paris.
   
   
   2.- A sentence which expresses duty or obligation:
   
   
   It is his duty to be in Paris.
   
   He is supposed to be in Paris.
   
   
   (In a similar way, "He should be in Paris" can be interpreted as both "I suppose he is in Paris" and "His duty is to be in Paris".)
   
   
   

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2. The verb need can be used with two different structures:
   
   
   1.- An ordinary passive sentence:
   
   
   We need to paint this fence.
   
   This fence needs to be painted.
   
   
   2.- A sentence with need as an active verb followed by a gerund as its direct object:
   
   
   This fence needs painting.
   
   

© Juan José Castaño