Explaining that water is wet is just a dormitive principle.
dormitive principle
idiomA type of tautology in which an item is explained in terms of the item itself, only put in different (usually more abstract) words.
Origin
first recorded 17th c.A modern translation of Latin, virtus dormitiva, coined by Molière in The Imaginary Invalid (1673). In the play, he lampoons a group of physicians providing an explanation in macaronic Latin of the sleep-inducing properties of opium as stemming from its "virtus dormitiva". The currency of this phrase as a critique of scientific claims is due to Gregory Bateson (1976, Steps to an Ecology of Mind p. 5), as is the translation of virtus as 'principle'.
The professor warned the students that defining a process by its own name is a classic dormitive principle.
By claiming that the medicine works because of its healing power, the author relies on a dormitive principle rather than providing a scientific explanation.