How can a mark on paper be called “space†when space is empty? One of the more confusing concepts of art is the concept of positive and negative space. It is easy to understand that the term “positive†has some relationship to putting lines and shapes on paper, but when you add the word “space†it becomes a concept that requires thought.
“Negative space†is even harder to get a handle on. In drawing classes, when people are told to pay attention to the shape of negative space, they are baffled. It sounds as if negative space should represent nothingness, so how can you give it a shape?
To understand positive and negative spaces in art, think of all spaces being equally full but containing different densities of matter.  Some matter (for example, a flowerpot) is dense enough to be seen with the human eye. Other matter (the air around the flowerpot) is so fine it can’t be seen. Scientists can tell you that the air is full of tiny particles of matter that is invisible to our eyes.
So “positive space†refers to “space that is occupied by something dense enough to be seen by the human eye†and “negative space†refers to “space that is occupied by matter so fine that it cannot be seen with the human eye.
This sounds pretty picky, and what does it have to do with drawing anyway? Just this: the person who thinks of air as being nothingness is disregarding its SHAPE. To draw objects in proportion and see the whole picture, we need to be able to see the shapes of the spaces around and between objects.
Let’s go back to our flowerpot (the positive shape). Imagine that a flower with leaves is growing in the pot. You can easily see the shapes of the flower and leaves. But now look at the shapes of the spaces between the leaves (where there is “nothing†but air).  By looking at these negative shapes, you can see exactly how far it is from one leaf to another, how far the leaves are from the stem, and what angles they fall at in relation to one another.
One of the keys to developing ability to draw is to treat positive and negative spaces as equal things to consider. By drawing the shapes of the spaces between the objects (negative space) as well as the objects themselves (positive space), artists solve proportion and composition problems, and become more accurate in their drawing, painting and sculpture.
Yes, even sculptors use negative and positive space. Stand in front of a mirror with one hand on top of your head and the bend your elbow stuck out as far from your ear as possible so your arm, neck, and head form a rough triangle. You can see the shapes of your head, arm, and shoulder — the positive spaces. Now look at the shape formed by the air inside the triangle of your head, neck, and arm. This is the kind of negative space sculptors deal with, and they have to be able to visualize it from all angles. Being able to see negative space is the difference between SEEING and just LOOKING.
Drawing negative spaces makes you aware of their sizes and importance. One exercise you can try is to place some objects against a white background, or in a window where the light is bright enough to reduce them to silhouettes. Then you can make studies of the negative shapes. Think only in terms of black and white — Try drawing something using only the negative shapes around the object or objects — don’t look at the object itself, just at the air around it!
Working with positive and negative shapes will increase your ability to observe and draw accurately.