안녕하세용~! -What does -서 do?- This little particle has the power to merge two sentences into one, serving as a 'because' or a 'so' equivalent. This particle illustrates a cause and effect relationship between two clauses of the sentence. -Where does -서 stand in the sentence?- -서 can be added to VERBS or ADJECTIVES, not nouns (!), in the 'cause' clause of the sentence. Basically, it'll all make sense in the examples :) Examples: 돈이 없어서 여행을 할 수 없어요- Because I don't have money, I