1. Van Gogh is referring here to J.J. Isaäcson’s recent writings on the analytical methods and laws of colour adopted by the neo-Impressionists: ‘De revolutionaire schildersgroep in Frankrijk’ (The revolutionary group of painters in France), De Portefeuille. Kunst- en Letterbode of 10 May 1890, pp. 75-76 and of 17 May 1890, pp. 88-89. Isaäcson mentions Van Gogh twice in a list of ‘emotional-impressionistic artists’, as he characterized them. In his closing sentence he says that he will discuss this ‘anti-official salon group’ in a subsequent article (p. 89). This explains Van Gogh’s remark later on in the letter that Isaäcson will perhaps mention him in a coming article.

Van Gogh views these articles as a ‘continuation’ of the series titled ‘Parijsche brieven’ (Paris letters), which Isaäcson had written in August-September 1889. On this subject, see letter 807, n. 2.

2. In October 1889 Van Gogh had made a similar request to Isaäcson; see letter 811.

3. Charles-François Daubigny is considered a forerunner of Impressionism. Normandian apple trees are a recurring theme in his extensive oeuvre. De Cock was influenced by the Barbizon School, to which Daubigny belonged. His influence is particularly discernible in De Cock’s Normandian landscapes.

4. Here Van Gogh is probably thinking of Olive trees (F 715 / JH 1759

) and Olive grove (F 585 / JH 1758

), see letter 805, n. 23.

5. Van Gogh is presumably referring here to Olive grove (F 586 / JH 1854

) and Olive grove with two olive pickers (F 587 / JH 1853

), to which he gave the same colour indications as in letter 834.

6. This description applies to the painting Olive trees (F 710 / JH 1856

); see letter 863.

7. Van Gogh had painted three variants of the olive trees ‘against a pink sky’: Women picking olives (F 654 / JH 1868

), Women picking olives (F 655 / JH 1869

) and Women picking olives (F 656 / JH 1870

). See letter 834.

8. Roses in a vase (F 681 / JH 1976

) and Roses in a vase (F 682 / JH 1979

9. Irises in a vase (F 678 / JH 1977

) and Irises in a vase (F 680 / JH 1978

10. For Pierre Puvis de Chavannes, Inter Artes et Naturam (Between art and nature), see letter 879, n. 15.

11. Reference to the Sermon on the Mount (Matt. 5-7). Van Gogh means that Puvis de Chavannes’s recent works contain the essence of his vision of society, just as the Sermon on the Mount is a summary of Christ’s teachings. Thus Van Gogh again endorses his old notion (formulated in letter 155) that modern art is a continuation of the gospel.