verb
to be on, to be awake
A1
Auf sein means primarily 'to be on' (a device) and colloquially 'to be awake.' It functions with the auxiliary sein and has the irregular participle 'auf gewesen.' Not reflexive. The particle is attached (not separable here) and the phrase follows the irregular conjugation patterns of sein.
Examples
Die Geschäfte sind heute auf.
The shops are open today.
Obwohl die Besucher schon gegangen waren, war das Licht im Flur auf, sodass die Nachbarn sich wunderten.
Although the visitors had already left, the light in the hallway was on, so the neighbors were puzzled.
Das Licht ist im Wohnzimmer auf.
The light in the living room is on.
Details
Mnemonics
Imagine a light switch labeled 'auf' in the ON position to recall 'auf sein' = 'to be on'.
literally 'up be' — think 'up' meaning active/on.
Notes
'auf sein' is a verbal phrase built with sein + particle. It is used idiomatically for things being 'on' (lights) and colloquially for people being awake (jemand ist noch auf). | Verbal phrase built with 'sein'; personal passive conjugation blocks are not applicable. Present participle for this verbal phrase is not normally used and is marked 'not applicable' in participles.präsens.