n. an unpractical theorist, disposed to carry principles to logical but unworkable extremes: in France, in 1815-30, one of a school who desired a constitution like that of Britain.—adj. theorist.—ns.
Chambers's Twentieth Century Dictionary (published 1908)
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One who would apply to political or other practical concerns the abstract doctrines or the theories of his own philosophical system; a propounder of a new set of opinions; a dogmatic theorist. Used also adjectively
Rather Alfonso and Father Octavio knew their Catholic dogma by rote; while the two priests talked circles around Brother Pepe, and they made Pepe feel inadequate in his belief, there were irreparably doctrinaire.
John Irving. Avenue of Mysteries, p.52 (2015)
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Note: In French history, the Doctrinaires were a constitutionalist party which originated after the restoration of the Bourbons, and represented the interests of liberalism and progress. After the Revolution of July, 1830, when they came into power, they assumed a conservative position in antagonism with the republicans and radicals.
They have, perhaps, when they look back upon their past lives, nothing to retract; they can, if they choose, publish a signed account of everything they have ever said or done; but they are poor creatures, feeble descendants of doctrinaires, and their wisdom is negative and sterile.