As history of thermodynamics say, it was a mystery that what is the required condition for a given energy conversion to take place? Like there are two possible events each conserving energy but only one is chosen. So, in order to resolve this Clausius introduced a quantity called entropy which was given by int(dq/T). But can I know the reason for which Clasius chose this integral or quantity, why not any other quantity (changes in whom, positive or negative, would decide the occurence of a given event)? I hope there lies an explanation to this which does not use statistical mechanics. Hoping for an answer.