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The CSI Method: C Curves, S Curves, and Straight Lines

A simple method for analyzing poses using C curves, S curves, and straight lines to improve gesture drawing.

Introduction

One of the hardest parts of figure drawing isn't the anatomy. It's figuring out what you're actually looking at.

When people first start drawing the human figure, the body looks like chaos. Arms twist, the torso rotates, the legs bend in different directions. It feels like there's too much information all at once.

I remember staring at poses during gesture drawing sessions and feeling completely stuck. I'd try to copy every shape I saw. The rib cage, the pelvis, the muscles, all of it. The drawing would quickly turn into a mess of lines.

Nothing connected.

Eventually someone showed me a simple trick artists use to simplify complex poses. It's called the CSI method.

CSI stands for three line types:

That's it.

These three shapes appear everywhere in the human figure. Once you start noticing them, figure drawing gets a lot easier. Instead of copying anatomy piece by piece, you begin describing movement using simple directional lines.

At first this method was something I had to consciously think about. I'd look at the pose and literally ask myself, "Is this a C curve, an S curve, or a straight?"

After enough practice though, something interesting happened. It became automatic. I stopped thinking about it.

Now when I look at a pose, the curves and straights are just... there.

The CSI method is especially useful when a pose feels confusing. When the body twists or overlaps in ways that are hard to read, breaking the figure into C curves, S curves, and straight lines gives you a simple starting point.

And once that first structure is clear, the rest of the drawing gets much easier.

What Is the CSI Method in Drawing?

The CSI method in drawing is a way to simplify the human figure by identifying three basic line types.

Artists use:

These shapes describe the direction and rhythm of the body.

Instead of drawing muscles right away, the artist looks for the dominant flow of the pose.

Here's what each line type represents:

C Curves

S Curves

Straight Lines

This approach works extremely well with gesture drawing. Gesture drawing focuses on movement and rhythm, not details.

The CSI method gives artists a simple system for analyzing poses quickly. Instead of guessing what's happening, you break the figure into a few clear directional lines.

Understanding C Curves in Figure Drawing

A C curve is one of the most common shapes in figure drawing.

It's simply a curve that bends in one direction. Like the letter C.

You'll see these everywhere in the human body.

Common places C curves appear:

When I first started practicing gesture drawing, I didn't notice these shapes at all. I was too focused on outlines.

But once someone pointed it out, I started seeing C curves everywhere.

One helpful trick is to follow the longest direction of a form. The torso often forms a big sweeping C curve when someone bends.

Another tip is to ignore small anatomy details and look for the overall direction of movement.

Ask yourself:

That big directional bend is usually your C curve.

Understanding S Curves in Gesture Drawing

If C curves describe simple movement, S curves describe rhythm.

An S curve changes direction once. It flows from one curve into another.

These appear frequently in dynamic poses.

You'll often see S curves in:

The human body naturally creates these shapes when balancing weight.

For example, when a person shifts their weight onto one leg, the pelvis tilts. The torso then compensates in the opposite direction.

This creates a natural S curve through the body.

Artists love S curves because they create flow. The eye moves along the shape smoothly.

When gesture drawings feel stiff, it's often because the artist ignored the natural S curves of the pose.

Using Straight Lines in Figure Drawing

A lot of beginners think figure drawing should be all curves.

But straight lines are just as important.

Straight lines add structure and contrast.

Common places straight lines appear:

Straight lines often appear in parts of the body that are supporting weight.

When combined with curves, they create a nice visual balance.

Think of it this way.

Curves show movement.

Straights show stability.

When both appear together, the pose feels believable.

How the CSI Method Helps Simplify Complex Poses

Sometimes you'll see a pose and think, "What is even happening here?"

Maybe the body is twisting. The arms overlap the torso. The legs cross.

This is where the CSI method becomes really useful.

Instead of analyzing everything at once, you ask a simple question.

What line types do I see?

Start by identifying the biggest movement in the pose.

Then look for:

Suddenly the pose becomes easier to understand.

Instead of chaos, you now see a structure of curves and straights guiding the body.

This makes gesture drawing faster and more accurate.

CSI Method and Line of Action

The CSI method works closely with another concept in figure drawing.

The line of action.

The line of action captures the primary movement of the pose.

In many cases that line will follow:

The CSI method helps you understand movement.

It reveals the underlying structure of the movement.

When both ideas are used together, gesture drawings become much clearer and more expressive.

Conclusion

Learning to see C curves, S curves, and straight lines can completely change the way you approach figure drawing.

The CSI method gives artists a simple way to simplify complicated poses. Instead of worrying about muscles and anatomy right away, you focus on movement, rhythm, and structure.

At first this method may feel like something you have to consciously think about.

You'll look at a pose and ask yourself which line types are present.

But after enough practice, something interesting happens. The process becomes automatic.

You begin seeing these shapes instantly.

And once that happens, gesture drawing becomes faster, clearer, and a lot more enjoyable.

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