A false doctrine is a Demon

DEMONS

The universal extension of the Greek language, Daimon, as understood by the Greeks, the Romans,—a “departed human ‘spirit’,” Natural gods of the heathens. The Cerriti and the Larvati. Beelzebub. Paul’s speech at Athens. Demons believe.
The worship of demons. Paul’s answer to the expediency, sham charity men of his day.
The word was born of superstition, a superstition still current among many people. Some backward people still believe that certain kinds of illnesses are due to the malignant influence of the spirit of a departed human being, taking possession of the afflicted person.
In some eastern countries, the same idea persists, and doctors find that their use of modern scientific methods is often useless unless the hypothetical "demon", the creation of imagination and superstition, is first "destroyed" or "cast out".
It is not unusual for modern medical men in the East to thus speak, in all seriousness, of "casting out a demon" when referring to the healing of such an afflicted person. They accommodate their description to an expression which conveys something to the mind of the natives. Norman Lewis in a book on Burma entitled Golden Earth records that such ideas are common among the Burmese.

Hippocrates, the physician of ancient Greece, wrote an essay on epilepsy, which was called the "sacred disease" because people believed the priests' teaching, that epileptics were possessed, and because priests, magicians, and impostors derived considerable revenue from attempting to cure the disease by expiations and charms. The essay was written to expose this delusion, he seeking to prove that this disease was neither more divine nor sacred than any other.

The Anointed One's conformity to popular language did not commit him to popular delusions. In one case, he apparently recognises the god of the Philistines: "You say that I cast out demons through Beelzebub: if I by Beelzebub cast out demons, by whom do your sons cast them. out?" (Luke 11:18, 19). Now, Beelzebub signifies the god of flies, a god worshipped by the Philistines of Ekron (2 Kings 1:6), and the Anointed One, in. using the name, takes no pains to dwell upon the fact that Beelzebub was a heathen fiction, but seems rather to assume, for the sake of argument, that Beelzebub was a reality; it was a mere accommodation to the language of his opponents. Yet this might, with as much reason, be taken as a proof of his belief in Beelzebub, as his accommodation to popular speech on the subject of demons is taken to sanction the common idea of "demons."

The casting out of demons spoken of in the Nazoraean Scriptures was nothing more or less than the curing of epileptic fits and brain disorders, as distinct from bodily diseases. Of this, any one may be satisfied by an attentive reading of the narrative and a close consideration of the symptoms, as recorded:--"Lord, have mercy on my son, for he is an epileptic and suffers severely; for he often falls into the fire, and often into the water. And I brought him to your disciples, and they could not cure him. . . . And Jesus rebuked the demon and he departed out of him (Matt 17:15-18).

From this, the identity of lunacy with supposed diabolical possession is apparent. The expulsion of the malarious influence which deranged the child's faculties was the casting out of the demon.

"Then was brought unto him one possessed with a demon, blind and dumb; and he healed him, insomuch that the blind and dumb both spoke and saw" (Matt 12:22).

"And one of the multitude answered and said, Master, I have brought unto you my son, because he has a speechless spirit" (Mark 9:17).

There is no case of demoniacal possession mentioned in the Nazoraean Scriptures, which has not its parallel in hundreds of instances in the medical experience of the present time. The symptoms are precisely identical--tearing, foaming at the mouth, crying out, abnormal strength, etc. True, there are no exclamations about the Messiah, because there is no popular excitement on the subject for them to reflect in an aberrated form, as there was in the days of Jesus, when the whole Jewish community was pervaded by an intense expectation of the Messiah, and agitated by the wonderful works of the Anointed One.

The transference of "the demons" to the swine, is only an instance in which the Messiah vindicated the Law (which prohibited the culture of the pig), by acting on the suggestion of a madman in transferring an aberrating influence from the latter to the swine, and causing their destruction. The statement that the demons made request, or the demons cried out this or that, must be interpreted in the light of a self-evident fact, that it was the person possessed who spoke, and not the abstract derangement. The insane utterances were attributable to the insanifying influence, and, therefore, it is an allowable liberty of speech to say that the influence---called in the popular phrase of these times, demon or demons--spoke them; but, in judging of the theory of possession, we must carefully separate between critical statements of truth and rough popular forms of speech, which merely embody an aspect, and not the essence of truth.
The Bible, therefore in using such terms as "casting out demons", merely accommodated its expressions to the current vernacular. To "cast out a demon" was to cure an illness.