Is fear a mental factor (caitta)?

Question: The mind of fear often arises. Is fear a mental factor (caitta)? Why is fear not listed among the mental factors in the One Hundred Dharmas? When one feels fear within, is it the mind consciousness that fears, or the manas? Some fears are inexplicable, arising without any cause—is that the manas being afraid? Answer: The mental activity of fear cannot be found among the fifty-one mental factors, because the varieties of mental factors in sentient beings are extremely numerous; the fifty-one mental factors are only a rough summary and do not include all mental factors, especially the very subtle ones. If all were included, there would be several hundred or more. The mental factors listed in the Mahāyāna Treatise on the One Hundred Dharmas are not complete; there could also be treatises on a thousand dharmas, ten thousand dharmas, or a hundred million dharmas. Beyond the hundred-dharma gate, there are extremely many dharmas not included. Therefore, fear is also a mental factor; it is simply that the hundred-dharma gate did not summarize it and include it. So in learning Buddhism and cultivating practice, we should not dogmatically assume that the dharma we currently encounter must be ultimate, unalterable, and inflexible. When a person or thing that causes fear comes to mind, it is first the manas that thinks of it; only when the manas cannot figure it out, or when it wants to do something, does it let the mind consciousness think about it in detail and react accordingly. Fear has two levels. Fear at the shallow level is the fear of the mind consciousness; it does not touch the root and does not produce effects or consequences on body and mind. Fear at the deep level is the fear of the manas; when severe, it is called terror, with great inner turbulence, producing reactions of varying degrees in the body, causing changes in breath, blood circulation, and neural transmission, which in turn induce pathological changes in the limbs and internal organs. After falling asleep, if the manas senses that something unexpected has occurred in the surrounding environment and feels fear and terror, it will prompt the six consciousnesses to wake up and find out exactly what frightening thing has appeared. When having a nightmare, if the manas is extremely frightened, it will make the mind consciousness wake up, no longer remaining within the nightmare. The fear of the mind consciousness and the fear of the manas are different. The fear of the mind consciousness does not induce various physical conditions, whereas when the manas is afraid, there will be bodily symptoms, such as trembling, a dreadful countenance, a tightening and quivering heart, accelerated blood flow, and so on. When the manas is afraid, there are also emotional reactions, such as a tense expression and inner anxiety. These symptoms indicate that it is the manas that is afraid. Fear of the mind consciousness alone is not real fear and will not cause bodily reactions. The manas can control the transmission nerves and direct the operation of the entire body, so when the mental activity of the manas stirs, the whole body reacts accordingly; but when the mind consciousness stirs, it cannot move the whole body, because the neural transmission throughout the body is directed by the manas, not by the mind consciousness. If the fear is inexplicable—if the mind consciousness feels that it is afraid yet does not know what it is afraid of, pondering over and over, "What am I afraid of?"—and it still feels fear without knowing what it fears, then it is the fear of the manas. The manas's fear cannot be explained clearly to the mind consciousness; the mind consciousness does not understand, yet simply knows that it is afraid. That is the fear of the manas—the fear deep within the heart is the fear of the manas.