Here are three similarities between neoclassicism, romanticism and realism.
They were all late 18th and 19th century European styles
As styles they were all formally based on Renaissance ideas about art, perspective, and color drawing composition etc.
The most important similarity is that they were all antagonistic interpretations of what art should be about; Neoclassicism about harmony, order and idealized form, Romanticism about individuality and emotion, Realism about society and the concrete realities of people’s lives.
