In English ergo is mostly used, if at all, in Latin phrases, as 'cogito ergo sum'. But whether 'ergo' or 'therefore' is used, it is important to realize that who uses it desires to indicate that what came before the 'ergo' or 'therefore' serves as a premiss or premisses, and what follows it is a conclusion. Also, the user suggests by using 'ergo' and 'therefore' that the premiss(es) entails the conclusion in a logically valid way, but this may be a mistake even if the suggestion is sincere.