An ostensive definition is a form of denotative definition. An ostensive definition is given by indicating the individuals, things or events to which the term applies. Ostensive definition explains the meaning of a word or phrase by pointing to what the word or phrase refers to.
Ostensive definitions are non-verbal. In an ostensive definition the definiendum is a term but the definiens is an object in the world. Ostensive definitions establish a link between words and objects in the world. It consists in the act of pointing to an example.
Suppose you point to a floppy disk lying on the table to explain to someone who does not know what the word “floppy” means. This will be a case of ostensive definition. Consider another example. Suppose that you are inside a zoo with your younger brother who has not seen a kangaroo yet. Pointing to a kangaroo you tell him, “Look, this animal is a kangaroo”. These are attempts to explain the meaning of terms by ostensive definitions.
An ostensive definition is
(a) Denotative, because the meaning is given by the set of individuals, objects, or events to which the term or expression can be correctly applied;
(b) Non-verbal, because the denotation of the term or expression is indicated non-linguistically (e.g., by pointing or displaying);
(c) Explicit, because the meaning of the term or expression is given entirely by, and nothing else but, the objects picked out by the act of ostension.
While ostensive definitions are often useful, they do not always work. Since ostensive definitions are denotative definitions, they share the limitations characteristic of denotative definitions. There are several other limitations of ostensive definitions as well.
Firstly, while explaining the meaning of a term to someone by pointing to it, the person’s attention might get directed to the wrong object.
Secondly, even if you succeed in identifying the right object by pointing to it, there remains the possibility that some special feature of the thing will mistakenly get identified in place of the thing itself.
Thirdly, the objects to be ostensively defined are not always available. For instance, you cannot ostensively define ‘ocean’ while in Koraput. Fourthly, the technique of ostensive definition is not suitable for abstract terms such as numbers, the gross national product, or the average worker.
In support of ostensive definitions it can be pointed out that there are cases where denotative definition is the only way we can explain the meaning of a term.
In any language there are some words we first learn by pointing at examples to which the term applies. Sensation words refer to relevant sense experiences. There is no other way to make their meaning clear.