Is fear a mental factor?

Question: The feeling 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 that fears? Sometimes fear arises inexplicably, without any cause—is it the manas that is afraid? Answer: The mental activity of fear cannot be found among the fifty-one mental factors, because the mental factors of sentient beings are of numerous kinds; the fifty-one mental factors are only a rough summary, and do not include all mental factors, especially the extremely subtle ones. If all were included, there would be several hundred or more. The mental factors listed in the Mahāyāna Hundred Dharmas Treatise are not complete; there are also gateways of a thousand dharmas, gateways of ten thousand dharmas, and gateways of a hundred million dharmas. Beyond the hundred dharmas, there are still extremely many dharmas not included. Therefore fear is also a mental factor; it is just that the Hundred Dharmas gateway did not summarize it or include it in its classification. So when we study Buddhism and cultivate practice, we should not dogmatically assume that the dharma we currently encounter is necessarily ultimate, unalterable, and inflexible. When one thinks of people or things that cause fear, it is first the manas that thinks of them; only when it cannot figure them out, or when it wants to do something, does it let the mind consciousness think in detail and respond accordingly. Fear is divided into two levels. Fear at the shallow level is the fear of the mind consciousness; it does not touch the root and does not cause effects or consequences on body and mind. Fear at the deep level, however, is the fear of the manas; in severe cases 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, the manas is extremely frightened and will make the mind consciousness wake up, no longer remaining within the nightmare. The fear of the mind consciousness differs from the fear of the manas. The fear of the mind consciousness will not induce various physical conditions, whereas when the manas fears, there will be bodily symptoms, such as trembling of the body, a bad complexion, tightening and throbbing of the heart, accelerated blood flow, and so on. The fear of the manas also has emotional reactions, such as a tense expression, inner anxiety, and so on. These symptoms indicate that it is the manas that is afraid. Fear of the mind consciousness alone is not true fear and will not cause bodily reactions. The manas can control the transmission nerves and direct the operation of the whole 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—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 cannot explain its fear clearly to the mind consciousness; the mind consciousness does not understand it, yet simply knows that it is afraid. That is the fear of the manas—the fear deep within the mind, which is the fear of the manas.