from Standpointmag:
Although Van Gogh's art was firmly rooted in realism (Dutch realism and the slightly sentimental, slightly moralising French realism of Millet; Italian art didn't get a look-in) there was an overwhelmingly romantic strain underlying this realism: Van Gogh believed fervently that paintings should concern themselves predominantly with stirring up powerful emotions, that colour, expressive in itself, could convey such emotions, and that accurate draughtsmanship was secondary. His visual metaphors were simple and powerful. Even the roots of a tree in sandy soil could "express something of life's struggle".
