An intensional meaning is one that lists the traits or attributes of a term. For example, the intensional definition of the world ‘turtle’ would be ‘has a shell, is a reptile, has four limbs’ and so on. An extensional definition is one that lists the members of the class that the term denotes. So, for ‘turtles’, the extensional definition would include snapping turtles, sea turtles, and every other member of the turtle family.
Examples of Intensional and Extensional Definitions:
Demonstrative, enumerative and definition by subclass are definitions that are based on extensions. Demonstrative definitions are ones that involve pointing to an object in order to define it. For example, when teaching a baby to speak, a parent may point to an object that way the baby knows which object is named what. A mother may point to a car and say ‘car’, and the mother may point to numerous types of cars (jeeps, vans, trucks) but will say ‘car’ for every one of them. An enumerative definition is one that names the members of the class that the term denotes. So the enumertaive definition of the term ‘author’ would be Ernest Hemingway, John Steinbeck, Hunter S. Thompson etc. A definition by subclass is a definition that names the sub-classes of a term. The word ‘clothing’ means either a sweater, pants, a jacket etc.
Synonymous, etymological, operational and definition by genus and difference are all examples of definitions that are based on intension. A synonymous definition is one that is synonymous with the first term. So a synonymous definition for the term ‘author’ would be ‘writer’. An etymological definition is one that describes the terms ancestry. The word ‘table’ is derived from the Old English word ‘tabule’, and ‘tabule’ was derived from the Latin word ‘tabula’. An operational definition is one that lists experimental procedures which are used to determine the being of a certain thing. An operational definition for ‘freezing’ could be ‘when a liquid is at or below 32 degrees Fahrenheit and has or is turning solid’. A definition by genus and difference is one that names the genus and a difference word of a term. For example, the term ‘window’ would be defined as a transparent (difference) glass (genus).