Absolute synonyms are regarded as very rare or even non-existent.
In the first place， some synonyms have the same denotative meaning but show differences in connotative meaning. Fox example， famous and notorious can be treated as synonyms because both of them have the denotative meaning of "well-known" but they have different connotation: famous has an appreciative meaning（positive value ）whereas notorious has a pejorative meaning（ negative value）.
In the second place， even when we focus on denotative meaning of words， we may find that some words appear to be synonymous but refer to slightly different sets of concepts or are used in slightly different contexts.
For example, "salary" and "wage" are two synonymous because both refer to "pay or financial reward given for the work one has done＂.But they are used in different situations. Salary usually pertains to money received by white-collar workers or by executives in managerial positions or by professionals. It is paid monthly. By contrast， wage is the amount of money that is regularly paid to someone or to a group of people for a particular type of work， especially manual or unskilled work.
Finally， some words are the same in meaning but have different collocations. For example， charge and accuse have the same denotation， but charge collocates with the preposition with， while accuse collocates with the preposition of.