 Implicature plays a well-attested diachronic role in grammaticalization and the origin of new meanings and  idioms.[24]  For example, metaphors have a typical life cycle: beginning as something a speaker means on a particular occasion; being picked up by others; catching on, which means becoming self-perpetuating and spreading through the population; and finally, dying and becoming a new lexical meaning or idiom. When dead, what used to be indirectly expressed is directly expressed. The term virus as applied to computers went through this evolution in the last few decades, originally denoting a biological organism that spreads from host to host, now having another meaning on which it denotes computer programs that spread from computer to computer in a similar fashion. When a dead metaphor has syntactic structure like go viral, it is an idiom. When metaphors become widespread and self-perpetuating, but are not yet idioms, they generate generalized conversational  implicatures.[25]