The polysemy of als lies mainly in its double role as a temporal and as a modal conjunction. In its latter function it may introduce a subordinate clause, a part of a sentence or a word; furthermore, it may occur in complex expressions (sowohl... als auch; insofern, als; zu... als dass).

In most cases the modal als introduces a comparison or a specification.

In its temporal sense, als usually introduces a subordinate clause referring to events that:

(a) occurred in the past simultaneously with the events expressed in the main clause, indicating a certain point in time,

(b) occurred in the past before the events expressed in the main clause,

c) occured in the past after the events expressed in the main clause.