In 1490, a 38-year-old artist in Milan did something unusual. He drew a man inside a circle and a square, surrounded by notes about proportions and measurements. We call it the Vitruvian Man.
What makes this interesting isn’t the drawing itself. It’s what his notebooks reveal about how he got there.
Because Leonardo da Vinci left us something rare: 7,200 pages documenting exactly how he thought.
And what those pages show is a pattern. A specific way of working that lets one person make breakthroughs in art, engineering, anatomy, mathematics, and physics.
This is Conscious Choice, my name is Lee Greene. And today we’re looking at what Leonardo’s notebooks actually tell us about how conscious choice and integration works.
So first, let’s talk about what we actually have.
Leonardo left behind roughly 7,200 pages of notes and drawings. That’s what survived. Scholars estimate he probably created three times that amount over his lifetime.
These aren’t casual sketches. They’re working documents. The Codex Atlanticus alone, stored in Milan, contains 2,238 pages spanning 40 years. The Codex Leicester has 72 pages just on water and geology. There are anatomical studies, engineering designs, mathematical problems, observations about light and shadow.
And here’s what matters: they’re dated. We can track his thinking over decades. We can see him return to the same problems years later with new understanding. We can watch his process evolve.
This isn’t speculation about what he might have thought. This is documentation of what he actually did.
Contemporary accounts back this up. Giorgio Vasari, writing 30 years after Leonardo’s death, interviewed people who knew him. He describes Leonardo’s working method: observation, notation, synthesis, then execution. Multiple sources confirm this wasn’t how other artists worked at the time.
So we have two layers of evidence. Leonardo’s own documentation of his process, and contemporary accounts describing how unusual that process was.
That’s rare. Most historical figures didn’t document their thinking this thoroughly. We’re lucky he was borderline obsessive about writing things down.
To understand why this matters, you need to know what intellectual work looked like in 1480s Italy.
The standard approach was specialization. You were a painter or a mathematician or an engineer. Not all three. And within each field, you followed established methods. Painters used traditional techniques passed down from masters. Mathematicians worked on classical problems. Engineers built what clients requested.
Innovation happened, but it was incremental. You improved on what came before.
Leonardo rejected this completely.
His notebooks show him moving between disciplines constantly. On a single page, you’ll find anatomical studies next to water flow patterns next to notes about painting techniques. To his contemporaries, this looked scattered. Unfocused.
But track it over time, and something else emerges.
The patterns he observed in water informed how he painted hair. His anatomical studies of muscles changed how he depicted movement. His mathematical work on proportions influenced his architectural designs.
He wasn’t scattered. He was integrating. Looking for patterns that crossed domains.
And he was doing this systematically. The notebooks aren’t random observations. They’re a documented practice spanning 40 years.
So let’s look at the actual process his notebooks reveal.
It starts with observation. But not casual observation. Systematic, almost obsessive attention to detail.
Take his anatomical work. Between 1507 and 1513, Leonardo performed about 30 human dissections. His notebooks from this period contain over 240 drawings of the human body.
But here’s what’s interesting: he didn’t just draw what he saw. Each drawing has notes. Questions. Measurements. Comparisons.
Look at his studies of the human heart. He drew it from multiple angles. Then he created a glass model and pumped water through it to understand flow patterns. Then he compared those patterns to water flowing in rivers.
This is documented. We have the drawings. We have the notes describing the glass model. We have his observations about the parallels between blood flow and water flow.
He’s not just observing. He’s testing. Measuring. Comparing across different contexts.
And he’s writing it all down.
Here’s a quote from his notes on anatomy: “You who say it is better to look at an anatomical demonstration than to see these drawings, you would be right if it were possible to observe all the details shown in these drawings in a single figure.”
He understood something crucial. Observation alone isn’t enough. You need to document it. Test it. Look at it from multiple angles over time.
His notebooks show this pattern repeatedly. Observe something. Draw it precisely. Ask questions about it. Test the questions. Document the results. Return to it later with new understanding.
That’s not just careful work. That’s a systematic practice.
And it’s only the first part of his process.
The second part is where it gets interesting.
Because Leonardo didn’t keep his observations separate. He was constantly looking for connections between different domains.
The notebooks show this explicitly. You’ll find pages where he’s drawing human musculature and, right next to it, sketching mechanical joints. Then notes comparing the two. “The arm operates on a lever system similar to this crane design.”
He’s not just observing anatomy and engineering separately. He’s synthesizing. Looking for underlying patterns that apply to both.
The Vitruvian Man is the most famous example. It’s not just an artistic drawing. It’s the integration of at least three different domains.
First, there’s the mathematical precision. He’s working from Vitruvius’s ancient text on proportions. His notes show the calculations: “The length of a man’s outspread arms is equal to his height.” Specific ratios. Measurable relationships.
Second, there’s the anatomical accuracy. This isn’t an idealized figure. The muscle structure is precise. The proportions reflect actual human bodies he’d studied through dissection.
Third, there’s the symbolic synthesis. The circle and square represent different concepts in Renaissance thinking – the divine and the earthly. He’s integrating philosophical ideas with mathematical and anatomical precision.
And his notes reveal this was intentional. He wasn’t accidentally bringing these things together. He was deliberately looking for where they connected.
Here’s another example from his engineering work. In the late 1480s, he designed a series of flying machines. The notebooks from this period show something specific.
He starts by observing bird flight. Detailed drawings of wing structures, notes about how birds angle their wings in different conditions, studies of how they take off and land.
Then he shifts to mechanical analysis. How could you build something that mimics these movements? What kind of joints would you need? What materials?
Then he tests smaller models. Documents what works and what doesn’t.
The final designs synthesize all of this. They’re not just copied from birds. They’re mechanical systems informed by natural observation, tested through iteration, refined based on what failed.
This is the integration part of his process. He’s taking precise analytical observation from multiple domains and synthesizing them into something new.
And again, this is documented. We can see it happening in real-time across the notebooks.
The third part of Leonardo’s process is what makes integration sustainable over decades.
He returned to the same problems repeatedly. With new understanding each time.
The Last Supper is a perfect example. We have contemporary accounts of how he worked on it between 1495 and 1498.
Matteo Bandello, who was a boy at the monastery while Leonardo painted, wrote about watching him work. Some days Leonardo would arrive early, climb the scaffolding, and paint continuously until dark. Other days, he would stand staring at the work for hours without touching it. Sometimes he’d add a single brushstroke and leave.
To the monks who commissioned it, this looked like inconsistent work. They complained to the Duke of Milan that Leonardo was lazy.
But Leonardo’s notebooks from this period show what was actually happening. He was iterating. Not just on the painting itself, but on his understanding of how to represent the moment.
His notes contain multiple studies of hand gestures. Different arrangements of the apostles. Calculations about perspective and how the viewer’s eye would move across the composition.
He wasn’t staring at the wall because he didn’t know what to do. He was integrating new observations into his existing work. Testing whether a new approach would improve what he’d already done.
And he had a specific method for this. His notebooks show it clearly.
First, he’d create multiple small studies exploring different approaches to the same problem. Then he’d analyze which worked better and why. Then he’d combine the best elements into a new version. Then he’d test that version against what he’d learned.
This is the recursive loop. Each iteration incorporates what the previous attempt revealed. And he documented the whole process so he could learn from it later.
Years after finishing The Last Supper, his notebooks show him still thinking about representation problems it raised. He’s taking lessons from that project and applying them to new work.
This pattern appears everywhere in his documentation. The Mona Lisa has four documented layers of paint, each refining the previous attempt. His engineering designs show multiple versions of the same mechanism, each incorporating what the previous version taught him.
Integration isn’t a one-time synthesis. It’s a practice you return to. Each time you engage with a problem, you bring new understanding. Each iteration makes the next one more informed.
Leonardo documented this process for 40 years. That’s not talent. That’s disciplined practice.
So what does this mean for us?
Leonardo lived 500 years ago. He didn’t have computers or AI or any modern tools. But the pattern his notebooks reveal is the same integration practice that works today.
Let’s break it down into specific steps you can actually use.
First, systematic observation. Leonardo didn’t just look at things casually. He observed with intention. He measured. He drew from multiple angles. He asked specific questions about what he was seeing.
For us, this means pausing before jumping to action. When you’re facing a problem or trying to understand something, take time to actually observe what’s happening. What are the actual facts? What can you measure? What can you verify?
Don’t just consume information passively. Engage with it the way Leonardo engaged with anatomy. Look at it from different angles. Test your understanding.
Second, cross-domain synthesis. Leonardo constantly looked for patterns that appeared in multiple fields. He wasn’t keeping his knowledge in separate boxes.
For us, this means asking: where else have I seen this pattern? How does what I know from one area apply to what I’m working on now? What connections exist that I’m not seeing because I’m thinking in categories?
This is active integration. You’re not waiting for insights to arrive randomly. You’re deliberately looking for where different pieces of knowledge connect.
Third, iterative refinement. Leonardo returned to problems repeatedly. Each time with more understanding.
For us, this means building in time for revision. Your first attempt at solving something reveals what you didn’t know. Your second attempt incorporates that learning. Your third attempt builds on both.
This isn’t a failure when your first version isn’t perfect. It’s a process. Leonardo’s notebooks show hundreds of “failed” attempts that led to breakthrough work. The attempts weren’t failures. They were iterations.
And fourth – and this might be the most important – document your process.
Leonardo’s notebooks weren’t just for record-keeping. They were tools for thinking. Writing things down forced him to be clear about what he observed, what he thought it meant, and what he still didn’t understand.
The act of documentation is part of the integration practice. You can’t integrate clearly if you’re not clear about what you’re integrating.
For us, this might be notes, sketches, recordings, whatever format works. But the practice of externalizing your thinking process is crucial. It lets you see patterns over time. It lets you return to problems with a fresh perspective. It makes the integration practice visible.
So what did this practice actually produce?
Over 40 documented years, Leonardo created:
- Roughly 20 major paintings that influenced Western art for centuries
- Engineering designs that weren’t understood until the 20th century
- Anatomical studies that advanced medical knowledge
- Mathematical work on geometry and proportion
- Studies of light, optics, and perspective that changed how art represented reality
- Observations about geology, water flow, and natural phenomena that proved accurate
That’s not output from one field. That’s unprecedented synthesis across multiple domains.
And here’s what matters: it wasn’t because he was a genius who spontaneously produced brilliant work.
His notebooks show the opposite. They show systematic practice. Disciplined observation. Constant iteration. Integration developed through decades of conscious effort.
The breakthrough work was the outcome of the practice, not the starting point.
This is documented. We can see it happening in real-time across 7,200 pages.
The Integration Practice – my book on thinking clearly in the age of AI – teaches this same pattern through modern tools.
But as Leonardo shows, the principles aren’t new. They’re not dependent on technology.
What AI does is make the need for integration visible. Because AI is a mirror. It reflects your thinking back to you. If you bring fragmented thinking, you get fragmented outputs. If you bring integrated thinking – observation, synthesis, iteration – you get something useful.
Leonardo used notebooks and drawings as his mirrors. We use different tools. But the practice is the same.
Pause before acting. Observe precisely. Synthesize across domains. Iterate deliberately. Document the process.
That’s integration. Leonardo proved it works.
Next time, we’re looking at Marie Curie. While Leonardo worked in Renaissance Italy with relatively few constraints, Curie practiced integration under extreme pressure.
Limited resources. Gender barriers. Personal tragedy. And maintained systematic thinking through all of it.
Her laboratory notebooks document exactly how she did it.
That’s next time on The Conscious Choice .
If you want to learn how these historical patterns apply to modern tools, the book is available wherever you get books. Link in the show notes.
Thanks for listening. This is Conscious Choice, this is Lee Greene.
@ 2025 Lee Greene