A simple technical distinction can help us better understand the wonders of Gothic architecture.
A gargoyle is simply the protruding part of a pipe that serves to deflect water that would otherwise accumulate on a roof. It is by no means a medieval invention: Egyptians, Greeks and Romans used them in ancient times, in order to prevent moisture from destroying their ceilings.
In fact, the French word gargouille is a derivative of the verb gargouiller, which in turn derives from the Greek gargarizó: to gargle. That is precisely what, as an architectural element, the gargoyle is in charge of: a gargoyle collects and then expels water away from the roofs and walls of the building. Technically speaking, the fantastic stone carvings that do not serve as functioning downspouts are known as grotesques, not gargoyles, though popular imagination lumps them together.
The celebrated historian and art critic Jurgis Baltrusaitis, one of the founders of the school of comparative artistic research and author of the book The Fantastic Middle Ages, is a constantly cited authority when it comes to the study of the presence of the monstrous in medieval art. Baltrusaitis explained that the half-human and half-animal creatures of antiquity never disappeared completely in Europe. The presence of the gargoyles, then, could be explained as a survival of these Greek and Roman motifs in later European art.