Positive space refers to the main focus of a picture, while negative space refers to the background. Negative space is more complex than simply the background of a picture. Without negative space, the positive would have no meaning.
I started to research Patrick Caulfield as an example of the use of negative space in art, and was immediately drawn to look at Matisse, by the notes in the course book that he had been one of Caulfield’s major influences.
Henri Matisse (1869 – 1954) Icarus 1946 http://www.tate.org.uk/about/press-office/press-releases/henri-matisse-cut-outs
When ill health prevented Matisse from painting in later life, he began to cut into painted paper with scissors to create outlines that take on sculptural form. Using vivid colours evoking the luminosity of stained glass, these cut-outs are a clear example of the use of negative space to suggest form. In this picture there is no actual detail of either the figure or the background, but somehow your eye fills in the gaps and almost creates detail that is not there.
Patrick Caulfield (1936-2005) is a 20th century artist who extensively explores the use of negative space in his art. His work tends to use flat blocks of colour and clear edges and lines; often flattening 3D forms into 2D shapes. In the following three images from http://www.tate.org.uk vases of flowers are reduced into just flat shapes and silhouettes.
In the Black and White Flower Piece (above) the black parts of the vase blend completely into the black background- although your eye tends to fill in the invisible shape based on the assumption that it will be symmetrical with the other white side of the vase. The flowers are suggested just by white shapes and by outlining and filling in areas of black shadow.
In this final picture, the vase and flowers seem to be simplified again, into flat, broad, black outlines and black shapes indicating shadow. I suspect that if there were no shadow under the vase, the picture would just look like a flat floral pattern. However, the shadow under the vase and the triangular grey area on the left of the picture, (indicating the edge of a table(?)), give this otherwise 2D image a sense of 3D form.
M. C. Escher was a master at creating drawings where there was no distinction between positive and negative space. Here is an example of Escher’s work which show the interplay between positive and negative space: