As It was explained to me the first organization was a secret literary society in the early 1800 s they used Greek letters for two reasons 1 universities taught ancient Greek and Latin among their course work so they were knowledgeable of the history and language of the ancient Greeks , and 2 it was a political statement in response to the monroe doctrine . Greece had just declared independence from the ottoman empire and the fraternity members wanted the us to support the independence movement spreading freedom and what not . The Monroe doctrine gave an excuse for the US to not intervene because Greece was in the eastern hemisphere and it stated the us sphere of influence only existed in the western hemisphere . The later organizations wanted to maintain this connection and so chose to continue using Greek letters . The letters usually correspond to some secret meaning the members know can ' t say if that is 100 % but it fits from what I ' ve seen .