The philosophies of Impressionists artists applied in their work were widely differ in styles compare to earlier periods. They advocated to work outdoors, create certain visual phenomena by intensive investigation, the study of dramatic effect of light and the etc.... to achieve revelation in technical discoveries.
The Expressionists artists works were more emotional, expressive and laden with emblem in a more scientific or intellectual approach. This trend was exemplified by Parisien artists which are Van Gogh and particularly Gauguin Impressionism style.
Which here I mean their work were Impressionism that go with expressive of emotional with emblem that is kind of similar to the Neoclassical-Romantic period where as in the Modern Art period, Expressionism could be Expressive + Impressionism which also signify the Post-Impressionism period.