Symbolism, as a movement beginning in the eighties, can be described as a reaction against naturalism which took on its classic form in about 1870 but had its roots in the sixties and, when seen in a larger perspective, was itself the final stage of realism already carried far by the preceding generation. In broader terms, symbolism can be thought of as part of a philosophical idealism in revolt against a positivist, scientific attitude that affected (or infected) not only painting but literature as well. Gustave Kahn in 1886 (the date of the last impressionist 'group exhibition') used as a foil the definition Zola had formulated in his defence of Manet: 'Our art's essential aim is to objectify the subjective (the exteriorization of the idea), instead of subjectifying the objective (nature seen through a temperament).' The symbolists themselves often thought in these terms, as witness Redon's well-known criticism of the 'low-vaulted ceiling' of impressionism, and Gauguin's complaint that it 'neglected the mysterious centres of thought'. And some of the impressionists felt the same way, notably Pissarro, who feared that the 'truth' of impressionism would be replaced by a sentimental, escapist 'aestheticism'.