What is called fashion is the tradition of the moment.

[Was man Mode heißt, ist augenblickliche Uberlieferung.]

Johann Wolfgang von Goethe (1749-1832) German poet, statesman, scientist

Sprüche in Prosa: Maximen und Reflexionen [Proverbs in Prose: Maxims and Reflections] (1833) [tr. Saunders (1893), “Life and Character,” sec. 7, #392]
    (Source)

(Source (German)). Alternate translations:

That which we call fashion is the tradition of the moment.
[tr. Rönnfeldt (1900)]

What we call fashion is momentary transmission.
[tr. Stopp (1995), "Posthumous," #986]