O que significa "outward costume" ?

Minha dúvida surgiu no trecho a seguir:
"By the 1780s we can take the existence of all these for granted, though
we cannot yet assume that they were sufficiently powerful or widespread.
On the contrary, we must, if anything, safeguard against the
temptation to overlook the novelty of the dual revolution because of the
familiarity of its outward costume, the undeniable fact that Robespierre's
and Saint-Just's clothes, manners and prose would not have
been out of place in a drawing-room of the ancien rSgime, that the
Jeremy Bentham whose reforming ideas expressed the bourgeois
Britain of the 1830s was the very man who had proposed the same
ideas to Catherine the Great of Russia, and that the most extreme
statements of middle class political economy came from members of
the eighteenth-century British House of Lords." ( The Age of Revolution i789-1848 - ERIC HOBSBAWM - FIRST VINTAGE BOOKS EDITION, AUGUST 1996, - p.3.)

O contexto está me sugerindo traduzir essa expressão por "aparência exterior"? Será isso mesmo? Em português, isso apesar de redundante , tem lá seu efeito estilístico. Será que o autor pretendeu usar de algum efeito com o emprego daquela expressão ou se referiu mesmo ao sentido literal das duas palavras? Dúvida... Quem tiver alguma, explicação agradeço. Obrigado