In the contemporary American English of adolescents and young adults (typically, females), the word like is a constant presence, mostly as a disfluent filler or discourse marker. Observation viva voce of raw speech specimens yields the following typology of functions of the word, in rough order of frequency.
(1) ticastic: for many speakers, the word is a verbal tic (whence the nonce adjective “ticastic”), replacing “you know” and its congeners, and having no other function than as a meaningless filler;
(2) phatic (perhaps as a sub-species of the ticastic): keeping the channel of communication open, sometimes for no other reason than to forestall a response from one’s interlocutor(s);
(3) quotative: as a prefatory marker before the report of someone else’s utterance(s) or inner speech;
(4) approximative: as a means of qualifying the extent or validity of the word or phrase immediately following, including its literal meaning;
(5) anaesthetic: as a way of deflecting the assertory force of anything following, usually as an apotropaism.
At bottom, all these modern-day extensions derive from and are parasitical on the word’s original meaning and its membership in the grammatical categories of adverb, preposition, and conjunction. What unites these originary uses is the fundamental sense of SIMILARITY underlying them. While it might be ontologically defensible to assert that some degree of similarity is characteristic of all relations, in this case what is being undermined is the very concept of IDENTITY. More precisely, the promiscuous extension of like in contemporary speech can be seen as yet another manifestation––here, linguistic––of the general historical tendency in American culture toward the LEVELING OF ALL HIERARCHIES.