Thesubjunctivemood,alwaysweakinEnglish,hasbeendwindlingawayforcenturiesuntilithasalmostvanished.Accordingtotraditionalthought,statementsabouttheconditionalfuturesuchas“IfIwereacarpenter...”requirethesubjunctive“were”;but“was”iscertainlymuchmorecommon.Still,ifyouwanttoimpressthoseintheknowwithyourusage,use“were”whenwritingofsomethinghypothetical,unlikely,orcontrarytofact.

　　Thesamegoesforotherpronouns:“you,”“she,”“he,”and“it.”Inthecaseofthepluralpronouns“we”and“they”theform“was”isdefinitelynonstandard,ofcourse,becauseitisasingularform.