The limitations of analogy in science and theology

Analogues have great value in helping us better understand difficult concepts. However, they do have limitations, and understanding those limitations can be helpful too. No analogy is perfect and if pushed too far can become problematic. In his chapter on Salvation in Theology: The Basics Alister McGrath points out this limitation and illustrates it with the notion of Jesus paying a "ransom" through his death (see Mark 10:45). The analogy is powerful because it illustrates that we were hostages to our sin without hope of freedom. Jesus death and resurrection liberates us. But if we push the analogy too far we start to get bogged down in questions such as "To who was the ransom paid? Who was the hostage taker who received the ransom payment: God or the Devil?".

Analogues have their value and limitations in science too. A famous and historically important one was that of the aether. In 1865 James Clerk Maxwell proposed that light is an electromagnetic wave analogous to a sound wave travelling through a solid or gas (a medium). But this analogy requires that there must be some medium in which the light wave is travelling. This medium was called the aether and Maxwell proposed it was a "sea of molecular vortices", which he sketched below.

Physicists searched for this new medium in vain. Eventually Michelson and Morley performed experiments that showed such a medium could not exist. Light waves travel in a vacuum. The analogy was helpful but limited.