From the Online Etymology Dictionary:
crucial – 1706, from Fr. crucial… from L. crux (gen. crucis) “cross.” The meaning “decisive, critical” is extended from a logical term, Instantias Crucis, adopted by Francis Bacon (1620); the notion is of cross fingerboard signposts* at forking roads, thus a requirement to choose.
“… given the nature of our intellectual commerce with works of art, to lack a persuasive theory is to lack something crucial— the means by which our experience of individual works is joined to our understanding of the values they signify.”
— Hilton Kramer in The New York Times, April 28, 1974
“I realized that without making the slightest effort I had come upon one of those utterances in search of which psychoanalysts and State Department monitors of the Moscow or Belgrade press are willing to endure a lifetime of tedium: namely, the seemingly innocuous obiter dicta, the words in passing, that give the game away.
What I saw before me was the critic-in-chief of The New York Times saying: In looking at a painting today, ‘to lack a persuasive theory is to lack something crucial.’ I read it again. It didn’t say ‘something helpful’ or ‘enriching’ or even ‘extremely valuable.’ No, the word was crucial….
The more industrious scholars will derive considerable pleasure from describing how the art-history professors and journalists of the period 1945-75, along with so many students, intellectuals, and art tourists of every sort, actually struggled to see the paintings directly, in the old pre-World War II way, like Plato’s cave dwellers watching the shadows, without knowing what had projected them, which was the Word.”
— Tom Wolfe, The Painted Word
For some related material from the next 30 years, 1976-2006, see Art Wars.
* “Note that in the original Latin, the term is not by any means ‘fingerpost’ but simply ‘cross’ (Latin Crux, crucis) – a root term giving deeper meaning to the ‘crucial’ decision as to which if any of the narratives are ‘true,’ and echoing the decisive ‘crucifixion’ revealed in the story.”