Van Gogh had no recollection of the event, suggesting that he may have suffered an acute mental breakdown. The hospital diagnosis was "acute mania with generalised delirium", and within a few days the local police ordered that he be placed in hospital care. Gauguin immediately notified Theo, who on 24 December had proposed marriage to his old friend Andries Bonger's sister Johanna. That evening Theo rushed to the station to board a night train to Arles. He arrived on Christmas Day and comforted Vincent, who seemed to be semi-lucid. That evening he left Arles for the return trip to Paris.
Theo criticised The Potato Eaters for its dark palette, which he thought unsuitable for a modern style. During Van Gogh's stay in Paris between 1886 and 1887, he tried to master a new, lighter palette. His Portrait of Père Tanguy (1887) shows his success with the brighter palette, and is evidence of an evolving personal style. Charles Blanc's treatise on colour interested him greatly, and led him to work with complementary colours. Van Gogh came to believe that the effect of colour went beyond the descriptive; he said that "colour expresses something in itself". According to Hughes, Van Gogh perceived colour as having a "psychological and moral weight", as exemplified in the garish reds and greens of The Night Cafe, a work he wanted to "express the terrible passions of humanity". Yellow meant the most to him, because it symbolised emotional truth. He used yellow as a symbol for sunlight, life, and God.
In July 1869 Van Gogh's uncle Cent obtained a position for him at the art dealers Goupil & Cie in The Hague. After completing his training in 1873, he was transferred to Goupil's London branch at Southampton Street, and took lodgings at 87 Hackford Road, Stockwell. This was a happy time for Van Gogh; he was successful at work, and at 20 was earning more than his father. Theo's wife later remarked that this was the best year of Vincent's life. He became infatuated with his landlady's daughter, Eugénie Loyer, but was rejected after confessing his feelings; she was secretly engaged to a former lodger. He grew more isolated, and religiously fervent. His father and uncle arranged a transfer to Paris in 1875, where he became resentful of issues such as the degree to which the firm commodified art, and was dismissed a year later.
Theo died in January 1891, removing Vincent's most vocal and well-connected champion. Theo's widow Johanna van Gogh-Bonger was a Dutchwoman in her twenties who had not known either her husband or her brother-in law very long and who suddenly had to take care of several hundreds of paintings, letters and drawings, as well as her infant son, Vincent Willem van Gogh.[note 14] Gauguin was not inclined to offer assistance in promoting Van Gogh's reputation, and Johanna's brother Andries Bonger also seemed lukewarm about his work. Aurier, one of Van Gogh's earliest supporters among the critics, died of typhoid fever in 1892 at the age of twenty-seven.
By this time van Gogh was ready for such lessons, and the changes that his painting underwent in Paris between the spring of 1886 and February 1888 led to the creation of his personal idiom and style of brushwork. His palette at last became colourful, his vision less traditional, and his tonalities lighter, as may be seen in his first paintings of Montmartre. By the summer of 1887 he was painting in pure colours and using broken brushwork that is at times pointillistic. Finally, by the beginning of 1888, van Gogh’s Post-Impressionist style had crystallized, resulting in such masterpieces as Portrait of Père Tanguy and Self-Portrait in Front of the Easel, as well as in some landscapes of the Parisian suburbs.