Some claim that the word “demon” in the New Testament is used as a figure of speech for mental or physical illness. Yet not one standard biblical lexicon, dictionary, or commentary defines the word that way. And keep in mind that these sources, in turn, derive their understanding from what the Bible itself says. It is also important to note that the Greek word for demon or demons should not be translated as Devil or devils, as the KJV sometimes does. There is only one Satan, called the Devil, whereas there are many demons. These are two different words and should not be confused.
For example, Thayer’s Greek Lexicon and BDAG (Bauer-Danker-Arndt-Gingrich) define daimonion as an evil spirit, demon, or hostile supernatural being. They do not define it as a metonymy or euphemism for an illness. Likewise, the verb daimonizomai (“to be demon-possessed” or “to be demonized”) refers to being under the power of a hostile spirit, not merely to having a psychological or physical condition.
The International Standard Bible Encyclopedia and The Holman Bible Dictionary both note that the New Testament distinguishes demon possession from ordinary disease. In Mark 5, Jesus delivers a man from a demon called Legion, followed by the healing of a woman and a little girl with various illnesses never called demons. In Luke 4, Jesus again delivers a man who has “an unclean demonic spirit,” followed by the healing of Simon’s mother-in-law from a fever, again not a demon. Matthew 4:24 likewise clearly shows separate groups of people suffering from distinct illnesses and others suffering from demons:
“So his fame spread throughout all Syria, and they brought him all the sick, those afflicted with various diseases and pains, those oppressed by demons, those having seizures, and paralytics, and he healed them.”
This text is especially clear, since it lists the demonized separately from those suffering from seizures, paralysis, and various pains. That distinction matters.
Luke 4:41 goes out of its way grammatically to show that the demons, not the people, are the ones crying out that Jesus is the Son of God. Similarly, in Mark 9:20, the demon is given personal agency in the narrative. Whatever grammatical arguments one makes in detail, the larger point remains: the text portrays demons as acting subjects, not merely as labels for illnesses.
The Gospel writers did not collapse everything into one general category of illness. Nor do the accounts themselves read like descriptions of mere mental or physical illness. The demonized often display distinctly supernatural features, such as recognition of Jesus’ identity, superhuman strength, fear of coming judgment, and multiple demons speaking through a single person. The latter is even identified by the name Legion (Mark 5; Luke 8). While some outward symptoms may overlap with epilepsy, insanity, or self-harm, the biblical narratives present demonization as something more than illness alone.
The same is true in Paul. In Ephesians 6:12, he states that “we are not wrestling against flesh and blood, but against the rulers, against the authorities, against the cosmic powers of this darkness, against the spiritual forces of evil in the heavenly places.” Note what Paul does not say: not that our battle is “not only against” human forces, but simply that it is “not against flesh and blood.” The Anchor Bible notes that some of the so-called Church Fathers, such as Jerome and Thomas Aquinas, failed to notice this particular feature of Ephesians 6. Instead, they explained the spiritual war as a battle against human passions or inner desires. But that is not Paul’s actual point in the passage. In Ephesians 6, the adversaries are not the self or fellow humans, but spiritual powers. Furthermore, the Greek term kosmokratores in Ephesians 6:12 was understood by both Jewish and Christian writers as referring to cosmic or demonic rulers in the heavenly realm. The term also fits with what Paul elsewhere calls the elemental spirits of the world in Galatians 4:3, 9 and Colossians 2:8, 20.
The New Testament account as a whole is quite straightforward. If someone wants to argue that “demon” really means mental illness, that argument is not coming from the standard lexical or dictionary evidence, which is based on the biblical accounts themselves. It is a redefinition imposed on the text. The recognized tools of biblical scholarship do not support it. They consistently define demons as evil spirits or hostile supernatural beings and distinguish demons from ordinary disease.
