Sosan, also known as Sengcan, was a Chinese Zen teacher who lived during the 6th century. He is considered the Third Zen Patriarch after Bodhidharma and Huike, and his teachings have had a profound impact on Zen Buddhism.

One of Sosan's most famous teachings is the "Hsin Hsin Ming" or "Verses on the Faith-Mind." This short poem, composed of 146 verses, is a profound expression of the essence of Zen. It emphasizes the importance of letting go of conceptual thinking and embracing the present moment as it is. Sosan wrote, "The Great Way is not difficult for those who have no preferences. When love and hate are both absent, everything becomes clear and undisguised."

Another well-known teaching of Sosan is the concept of "no-mind" or "wu-hsin." This refers to a state of mind that is free from thoughts, judgments, and attachments. Sosan believed that this state of no-mind is the true nature of our being, and by letting go of our ego and thoughts, we can experience true enlightenment.

Sosan also emphasized the importance of meditation and self-inquiry in the path to enlightenment. He wrote, "The mind is the root from which all things grow. If you can understand the mind, everything else is included. It's like the root of a tree. All a tree's fruit and flowers, branches and leaves depend on its root. If you nourish its root, a tree multiplies. If you cut its root, it dies."

In addition to his teachings, Sosan also wrote commentaries and letters to his students. One of his most famous letters is the "Letter to Huike," in which he describes the true nature of Zen and the importance of direct experience over intellectual understanding. He wrote, "The ultimate Truth is beyond words. Doctrines are words. They're not the Way. The Way is wordless. Words are illusions. They're no different from things that appear in your dreams at night, be they palaces or carriages, forest or cities."

Sosan's teachings continue to be studied and practiced by Zen practitioners around the world. His emphasis on the present moment, letting go of the ego, and direct experience have had a profound impact on the development of Zen Buddhism. As he wrote, "If you want to see the truth, don't think. To understand fully, let the mind be empty. Stop all activity. Be still and abide in the original state."