At/In (~time, place)

The core concept: In English, you use prepositions like "at," "on," "in" for both time and place almost interchangeably, and the distinction feels semantic rather than grammatical. Korean forces you to think differently: 에 marks a destination or a point in time—it's about *where/when something is located or happens*. This is fundamentally different from English thinking.

When English speakers say "I am at 3 o'clock" or "I am in Seoul," these feel like awkward phrasings because English doesn't mark them grammatically the same way. Korean does: 나는 3시에 있어요 (I am [at] 3 o'clock) and 나는 서울에 있어요 (I am [at] Seoul) use the same particle 에 because both express a location or point in time where the subject exists or an action occurs. This is the WHY: 에 isn't just a preposition—it's a grammatical marker that treats time and place as equivalent concepts in Korean thought.

The key difference from English: English relies on context and variety of prepositions (at, in, on, during, etc.). Korean reduces this to a system: 에 for destinations and time-points, 에서 for the active location where an action takes place. For example, "I study at the library" uses a location (library), so it's 도서관에서 공부해요 (the action happens *at* the library). But "I go to the library" is 도서관에 가요 (direction/destination toward the library). English doesn't force this distinction grammatically—Korean does. This trains your brain to always consider whether you're talking about a location/time where something exists, or where an action happens.

Understanding 에 means understanding that Korean collapses time and space into one grammatical system—both are "locations" in Korean thinking, and 에 marks them neutrally. This is radically different from English, where temporal and spatial prepositions feel separate.