Zen as we know it today is the result of a long history, with many changes and contingent factors. Each period had different types of Zen, some of which remained influential while others vanished. There are two main types, Chinese and Japanese.
From Bodhidharma in the late 5th century to the An Lushan Rebellion around 765 CE, in the middle of the Tang Dynasty. Little written information is left from this period. It is the time of the Six Patriarchs, including Bodhidharma and Huineng, and the legendary “split” between the Northern and the Southern School of Chán.
From the end of the An Lushan Rebellion around 765 CE to the beginning of the Song Dynasty around 950 CE. This was the time of the great masters of Chán, such as Mazu Daoyi and Linji Yixuan, and the creation of the yü-lü genre, the recordings of the sayings and teachings of these great masters.
Arouns 950 to 1250, which spans the era of the Song Dynasty (960-1279). In this time the gongan-collections were compiled, collections of sayings and deeds by the famous masters, appended with poetry and commentary. This genre reflects the influence of literati on the development of Chán. This period idealized the previous period as the “golden age” of Chán, producing the literature in which the spontaneity of the celebrated masters was portrayed.
So what is Zen exactly?
Zen is very simple, and asks the main question: What are you?
In this whole world everyone searches for happiness outside, but nobody understands their true self inside.
Everybody says, “I” – “I want this, I am like that…” But nobody understands this “I.” Before you were born, where did your I come from? When you die, where will your I go? If you sincerely ask, “what am I?” sooner or later you will run into a wall where all thinking is cut off. We call this “don’t know.”
Zen is keeping this “don’t know” mind always and everywhere.
Finally, your don’t-know mind will become clear. Then you can see the sky, only blue. You can see the tree, only green. Your mind is like a clear mirror. Red comes, the mirror is red; white comes the mirror is white. A hungry person comes, you can give him food; a thirsty person comes, you can give her something to drink. There is no desire for myself, only for all beings. That mind is already enlightenment, what we call Great Love, Great Compassion, the Great Bodhisattva Way. It’s very simple, not difficult!