By A.E. Waite (1911), tarot card illustrations by Pamela Colman Smith (1911)
Ravage, violence, vehemence, extraordinary efforts, force, fatality; that which is predestined but is not for this reason evil.
Divinatory Meanings – Reversed
Evil fatality, weakness, pettiness, blindness.
The design is an accommodation, mean or harmony, between several motives mentioned in the first part. The Horned Goat of Mendes, with wings like those of a bat, is standing on an altar. At the pit of the stomach there is the sign of Mercury. The right hand is upraised and extended, being the reverse of that benediction which is given by the Hierophant in the fifth card. In the left hand there is a great flaming torch, inverted towards the earth. A reversed pentagram is on the forehead. There is a ring in front of the altar, from which two chains are carried to the necks of two figures, male and female. These are analogous with those of the fifth card, as if Adam and Eve after the Fall. Hereof is the chain and fatality of the material life.
The figures are tailed, to signify the animal nature, but there is human intelligence in the faces, and he who is exalted above them is not to be their master for ever. Even now, he is also a bondsman, sustained by the evil that is in him and blind to the liberty of service. With more than his usual derision for the arts which he pretended to respect and interpret as a master therein, Éliphas Lévi affirms that the Baphometic figure is occult science and magic. Another commentator says that in the Divine world it signifies predestination, but there is no correspondence in that world with the things which below are of the brute. What it does signify is the Dweller on the Threshold without the Mystical Garden when those are driven forth therefrom who have eaten the forbidden fruit.
15. The Devil. In the eighteenth century this card seems to have been rather a symbol of merely animal impudicity. Except for a fantastic head-dress, the chief figure is entirely naked; it has bat-like wings, and the hands and feet are represented by the claws of a bird. In the right hand there is a sceptre terminating in a sign which has been thought to represent fire. The figure as a whole is not particularly evil; it has no tail, and the commentators who have said that the claws are those of a harpy have spoken at random. There is no better ground for the alternative suggestion that they are eagle’s claws. Attached, by a cord depending from their collars, to the pedestal on which the figure is mounted, are two small demons, presumably male and female. These are tailed, but not winged. Since 1856 the influence of Éliphas Lévi and his doctrine of occultism has changed the face of this card, and it now appears as a pseudo-Baphometic figure with the head of a goat and a great torch between the horns; it is seated instead of erect, and in place of the generative organs there is the Hermetic caduceus. In Le Tarot Divinatoire of Papus the small demons are replaced by naked human beings, male and female ‘ who are yoked only to each other. The author may be felicitated on this improved symbolism.
By S. L. MacGregor Mathers, c 1888
The Devil – Fatality for Good.
Divinatory Meanings – Reversed
Fatality for Evil.
Symbolism of the Keys
The Devil – A horned and winged demon with eagle’s claws (standing on an altar to which two smaller devils are bound by a collar and cord). In his left hand he bears a flame-headed sceptre. He is the image of Fate or Fatality, good or evil.
General Book of the Tarot
By A. E. Thierens, 
Description and Meaning
The goat-like figure recalls the sign Capricorn in which astrology teaches that the planet Mars has its exaltation, the name ‘devil’ means the evil, as is well known, and this alliteration holds good not only in English. It is the symbol of that which to exoteric human understanding is as much of a malefic nature as Venus is benefic. The counterpart of Venus: Mars, planet of pain and struggle, passion and sex-nature, but also of the energy necessary for the process of formation and generation in Nature. Allusion to sex-problems is found in the two human figures, man and woman, chained to the pedestal on which the diabolic figure is seated. That sex-nature binds man, is a natural fact of a more or less occult order.
So it has to do with generation in Nature in every sense and kingdom, though astrology teaches that Mars has a special connection with the animal kingdom and animal passion–passion which drives to the preservation of the body as well as of the race; fighting for existence in both senses of the term. So Mars always figured as the War-lord. Not only sexual energy, but every energy in Nature chains the result to the cause and object to subject. It is unnecessary to work this out any further. We shall be safe in interpreting this card as energy, desire, lust, war, struggle, difficulties, pain, loss, etc. But also as exercise, training; tests to which the personality will be subject.
The torch in the hand of the figure denotes, of course, the fire of passion and desire, which may rise to anger, etc. So it may well be said to represent the condition of “Adam and Eve after the Fall” (Waite) The struggle for existence, in short.
Papus in regard to this card points to the Hebrew letter “Samech which expresses the same hieroglyphic sign as the Zain (7th arcanum) . . . etc., a weapon of any kind . . .” We can see, that this generative force has much to do with the house of marriage.
By Paul Foster Case (1933)
15, Le Diable
Corresponds, through the letter Ayin, with Capricorn. In all but the highest spiritual questions, where the Querant is definitely and consciously on the occult path, this card is of evil significance. In its most general meanings, it signifies Mammon, and thus big business, the conventions of society, the injustice and cruelty of a social order in which money takes the place of God, in which humanity is bestialized, in which war is engineered by greed masquerading as patriotism, in which fear is dominant. Students of astrology will have no difficulty in seeing how this corresponds to Capricorn, the sign of big business, and the sign of worldly fame. Not that Capricorn is evil, but that its lower and negative expression is what has just been mentioned.
Bondage, materiality, force (especially the force of convention and public opinion), fate, necessity.
More information on The Devil Tarot card.