Composition is how you arrange things in the picture. The same tree can make a dull picture or a lively one depending only on where you put it.
The rule of thirds is a simple starting tool. Divide the picture into thirds across and thirds down, like a tic-tac-toe grid. Placing the main subject near one of the lines, or where two lines cross, often looks livelier than placing it dead center. A horizon on the upper or lower third line usually looks better than one that cuts the picture exactly in half.
A tree near the left third line, the horizon near the lower third line. The buttons show other guides.
🔑 Key idea
Divide the picture into thirds both ways. The subject near a third line or a crossing, and the horizon on a third line, often look more lively than dead center. It is a guideline, not a law.
💡 Why it works
A subject in the exact center feels settled and still, and a horizon in the middle splits the picture into two equal halves that compete. Off center, the spaces are uneven, and uneven spaces move the eye around the picture. The name "rule of thirds" was first printed in 1797 by the English artist John Thomas Smith, in a book about drawing landscapes.
✏️ Worked example: Finding the lines
Your paper is 30 cm wide and 21 cm tall. Where are the third lines?
Across: 30 ÷ 3 = 10, so vertical lines at 10 cm and 20 cm from the left edge.
Down: 21 ÷ 3 = 7, so horizontal lines at 7 cm and 14 cm from the top.
Answer: Vertical lines at 10 and 20 cm; horizontal lines at 7 and 14 cm.
✏️ Worked example: Sky or ground?
In a landscape, the horizon sits on the upper third line. What does the picture show more of?
Above the upper third line is one third of the picture: the sky.
Below it are two thirds: the land.
Answer: More land than sky.
⚠️ Common mistake
Some people treat the rule of thirds as a law and think a centered subject is always wrong. It is not. Portraits, symmetrical buildings and calm scenes are often centered on purpose. Use thirds when you want movement and centering when you want stillness, and choose on purpose.
Ruisdael's Windmill at Wijk bij Duurstede sets its low horizon well below the middle, so the big sky and the windmill fill most of the picture.
The Windmill at Wijk bij Duurstede, by Jacob van Ruisdael.
Practice
Pass with 3 right answers, the last 2 in a row. Each right answer earns 1 XP.