An analogy is a similarity between things.

In an argument from analogy, one argues from

known similarities to further similarities. Such

arguments often occur in philosophy. In his Dialogues

Concerning Natural Religion, David Hume

considers an argument from analogy that purports

to show that the universe was created by an

intelligent being. The character Cleanthes claims

that the world as a whole is similar to things like

clocks. A clock has a variety of interrelated parts

that function together in ways that serve ends.

The world is also a complex of interrelated parts

that function in ways that serve ends, such as providing

food for human consumption. Clocks are

the result of intelligent design, so, Cleanthes concludes,

probably the world as a whole is also the

product of intelligent design. Hume’s character

Philo criticizes the argument. In “The Argument

from Analogy for Other Minds,” Bertrand Russell

uses an argument from analogy to try to justify

his belief that other conscious beings exist.

Arguments from analogy are seldom airtight.

It is possible for things to be very similar in some

respects, but quite different in others. A loaf of

bread might be about the same size and shape as a

rock. But it differs considerably in weight, texture,

taste, and nutritive value. A successful argument from analogy needs to defend the relevance of the

known analogies to the argued for analogies.