Thousands of explanations have been offered for typical dreams which almost every one has had at least once, such as dreams of falling or flying, but none of them should be accepted as covering all cases. The human mind is compelled to do its thinking along certain lines and to use certain categories like time, space, etc. Naturally, dreams, which are in no way different from waking thoughts, must move along certain definite grooves too; but we must remember that no symbol has an absolute meaning. Every symbol is likely to have a slightly different meaning for every individual. We shall see in the chapter on "Attitudes in Dreams" that it is the type of dreams rather than their content which is important psychologically. And it is the type of man who dreams which is important to bear in mind when we try to ferret out the meaning of a typical dream. Generally speaking, flying dreams seem to correspond to one of the most universal cravings of mankind: to liberate itself from the tyranny of the law of gravity and enjoy the freedom which winged creatures enjoy. All races have wished to fly and that desire, never gratified in waking life until recently, was bound to express itself in the dreams of all races at all periods of history. Freud has suggested that such dreams repeat memories of childhood games, rocking, see-sawing; Federn has seen in them a symbol of sexual excitement, both of which explanations sound unconvincing. There may be a symbolism of a different sort about flying dreams. If for some reason or other, our sleep becomes suddenly much deeper, we may represent our "flight" from reality through a flight through the air. We soar to the dream level which we feel to be higher than the waking level, to which on awakening, we fall painfully. Variations in the sleep depth would thus account for the frequent relation of sequence which is observable between flying and falling dreams. Flying dreams are never connected with any fear of anxiety, while falling dreams are almost always nightmares of usually short duration. The Freudians see in many falling dreams memories of falls in childhood. "Nearly all children," Freud writes, "have fallen occasionally and then been picked up and fondled; if they fell out of bed at night, they were picked up by their nurse and taken into her bed." This explanation fits only an insignificant number of cases. The symbolism of the falling dream is found upon analysis to be much richer. In women, dreams of falling are very often symbolical of sexual surrender. Anxiety or pleasure connected with falling dreams reveals the fear or pleasure connected with such a thought in the dreamer's mind. Not a few falling dreams transform themselves after a slight period of anxiety into flying dreams, thus indicating that the feeling of inferiority connected with the idea of surrender was very slight and easily replaced by a feeling of power, freedom and superiority to environment and conventions.