General Book of the Tarot, by A. E. Thierens, , at sacred-texts.com
TRADITION: Young man, friendly. Departure, absence, flight, emigration, change of residence, desertion, transmigration, transplantation, transmutation, separation, disunion, rupture, discontinuance, brouillerie, discord.
THEORY: The workings of Air by a special and mighty agent--for this the knight is in all cases--on the houses of water, here the Fourth and the
[paragraph continues] Twelfth, causes turbulence, motion, emotion (though it must be borne in mind, that it is not emotion in itself); the action of the air on the water causes waves. In the case of the fourth house the knight relates to family matters or household conditions, eventually the father, to internal conditions in society or groups of people. It must further relate to memories and the past in general, because it means the awakening of the sentiments. The traditional conclusions have been drawn evidently in the negative for the greater part, in consideration of the fact that the sentiments generally are misleading. That they give reason for many changes is quite true. In the case of the twelfth house this is much the same. But extending its result over a much larger circle, the mercurial knight may represent expedition and exploration, discovery, scientific or practical, emigration, estrangement, and the 'great work' of transmigration. It denotes a searching for the unknown, which in weak personal cases may appear as indiscretion or premature revelation, divulgation, profanation, etc. We do not see why this knight should be either young or friendly.
Quite the reverse: On account of the twelfth house there is something inimical about him, and a certain dissension of sentiment may find its cause in the past, in a family feud or something in the nature of a misguiding prejudice, tradition, which will have to be given up, etc.
CONCLUSION--(From the fourth house): A representative of the father, or of the family, a relative; a man visiting the house bringing new and perhaps disturbing influences into it, disturbing domestic happiness;
changes in the home, house or family; memories awakened, divulgation of family secrets or private matters; an intruder in the home. A man of doubtful though not necessarily bad character. (From the twelfth house): An investigator, occultist, explorer, sailor, traveller on the high seas, wanderer, a guide through strange experiences, vagrant Bohemian type, stranger and sometimes enemy or some one with whom the querent does not agree and from whom he will be estranged, however earnest his endeavours to keep friendly, because he speaks either morally or physically a foreign tongue. Translation, export, departure, change of residence, emigration, flight, absence, rupture, etc. Transmutation. Disturbing influences and people in general, which need not be bad in itself, and may even cause a revolution in thought. It brings unrest in any case.