So is an english word that, apart from its other uses, has become increasingly popular in recent years as a coordinating conjunctive opening word in a sentence. You use so when you are saying that something which has just been said about one person or thing is also true of another one. In formal english, so is not used as a conjunction, to indicate either purpose (he left by a back door so he could avoid photographers) or result (the project was abandoned so his services were no longer.