Definitions from "This Means That" Ch 1

Sign: Form of communication in things that are not always transparent to us. Composed of the signifier and signified and are sometimes arbitrary.

Ex: Woof = barking = dog.

Dog = Understandable to language = Four-legged animal

Index: The non-arbitrary part of a physical causal relationship between the signifier and the signified

Ex: Ticking is caused by a clock.

A black eye is caused by a punch.

Symbol: Any sign where there is an arbitrary relationship between the signifier and signified.

Ex: A black tie = Arbitrary relationship = A formal occasion.

Brrrr = Arbitrary relationship = It's cold outside.