"Vulgarism" (also called scurrility) derives from Latin vulgun, the "mean folk", and has carried into English its original connotations linking it with the low and coarse motivations that were supposed to be naturally endemic to the meaner classes, who were not moved by higher motives like fame for posterity and honor among peers—motives that were alleged to move the literate classes. Thus the concept of vulgarism carries cultural freight from the outset, and from some social and religious perspectives it does not genuinely exist, or—and perhaps this amounts to the same thing—ought not to exist.
In Medieval times, "vulgar" referred to texts written in a vernacular instead of Latin, which was the standard language of literature, science, and theology at the time. During Late Antiquity "vulgar Latin" was used to refer to the vernacular dialects that sprang from Latin across the Roman Empire—the predecessors of the modern Romance languages.
The major step in the liberation of academia from Latin was the Protestant Reformation which advocated giving Mass and reading from the Bible in vulgar languages. Following in the footsteps of the Reformation, some proponents of the scientific revolution began to establish the precedent for writing in vulgar. However, as understanding of one or more the classical languages had been a commonality among the educated in the Western World, this switch to the vulgar also had the effect of limiting the accessibility of texts. Scholars who did not share the native language of the author would have had access to the work had it been produced in one of the "universal" classical languages. Texts were just too expensive to produce in more than one language (with the exception of the Bible, since it was virtually guaranteed to sell). In effect, this ironically limited the spread of knowledge among the wider world of scholars, while marginally increasing the spread of knowledge among the uneducated in the authors' home country who shared use of the vulgar but often could not read it. It was not until wide-spread literacy, mass-produced print, and easy translation came about many years later that the vernacular became instrumental in the general spread of knowledge.
Although most dictionaries offer "obscene word or language" as a definition for vulgarism, others have insisted that a vulgarism in English usage is different from either profanity or obscenity, cultural concepts which connote offenses against a deity and the community respectively. One kind of vulgarism, defined by the OED as "a colloquialism of a low or unrefined character," substitutes a coarse word where the context might lead the reader to expect a more refined expression: "the tits on Botticelli's Venus" is a vulgarism.
More broadly, as "vulgarity" generally has a social and moral component. Whether deliberate or accidental, the substitution of a commonplace word that is not a mere euphemism. It draws attention to a speaker's high-toned moral superiority or sophistication. Some fatal flaw in the usage often reveals that the speaker's ambitions are not based in reality: vulgarisms highlight the pretentious, showing that people lay unwarranted claim to social graces and education and attempt to inflate their status through the use of language they either cannot control or do not understand.
Several examples will be instructive.
A case in point is objets d'art which denotes ornamental decorative objects of little practical use but considered by the user to be of some artistic merit and material value. The phrase is taken from 19th-century English auctioneers' puffery, with the assumption that if it were French it was of a higher standard of artistry. "Objects d'art" is a gaffe aiming at the French objets d'art ('artistic objects' ). It appeared in Rothschild wills published in the late 19th century, and it is an expression now in common English usage. Like most vulgarisms, it is a shibboleth, defining the status of the speaker.
The substitution of homes for brick-and-mortar houses had its origins in real estate salesman's pitch which implied that the hearth or foyer of family life could be bought in the market, ready-installed in its architectural shell. The inflation was a vulgarism for at least two generations. Today it has gained such wide acceptance that it simply distinguishes middle-class from upper-class usage; or as Nancy Mitford, an expert on the subject, would have said 'U' from 'Non U' usage.
Thomas Carlyle equated vulgarism with materialism when he wrote "The deepest depth of vulgarism as that of setting up money as the ark of the covenant". The religious image that he used is a clue that for Carlyle vulgarism had an inescapable moral component, and its specific Old Testament origin evoked the image of the Philistines in their 21st-century connotation, the embodiments of Philistinism.