What did Leonardo da Vinci mean by saper vedere?

For Leonardo da Vinci, the phrase saper vedere—translated as "knowing how to see"—was the central theme of his intellectual life and scientific inquiry.1

Leonardo considered sight to be the most important human sense, as he believed it provided the most immediate, accurate, and certain access to the facts of experience. By saper vedere, he meant the disciplined, rigorous practice of visual observation used to probe the secrets of nature. Rather than relying on speculative book knowledge, he prioritized the irrefutable facts gained through this direct, empirical study of the visible world.123

This concept was fundamental to his synthesis of art and science. He believed that by observing objects, recognizing their form and structure, and carefully reproducing them, the artist could achieve true knowledge. Consequently, he viewed painting as a science, asserting that the painter—endowed with the ability to observe and pictorialize the world—was uniquely qualified to understand and describe nature exactly as it is.4