One of the first things to decide in a composition is how many elements or items there will be in it. And one of the simplest ways to make a composition more dynamic is to have an odd number in the composition, say three, five, or seven, rather than an even number, say two, four, or six. It's called the Rule of Odds.
Having an odd number of things in a composition means your eye and brain can't pair them up or group them easily. There's some how always one thing left over, which keeps your eyes moving across the composition.
With an even number of elements, such as in the basic composition show in the top image, your eye instinctively pairs up the trees, whether it's two left and two right or two top and two bottom. Whereas the lower two compositions, each with an odd number of elements, are more dynamic in terms of composition, because your brain can't pair up the elements.
Why do we pair things up naturally? Perhaps it's because our body is designed in pairs: two eyes, two ears, two arms, two hands, and so on. (Okay, we've only one nose, but it's got two nostrils!)
Does It Make a Difference What I'm Painting?
No, whether it's bottles, apples, trees, or people, the same Rule of Odds applies. Of course, the number of elements is not the only thing to consider in a composition, but it's essential and quite a good starting point for developing a painting.
Take a look at an example of the Rule of Odds in a painting...