These words refer to anything serving or used to accomplish a purpose. Means is the most general word. In a concrete sense, it points to a device or contrivance used to carry out an action or perform an operation.

• A hammer is a means of driving a nail; A taxi was his means of getting to the theatre.

In a broader, abstract sense, it refers to method, system or technique: the means by which a politician may extend his power.

• The harnessing of falling water is a means of generating electricity; Statistical analysis is a means of arriving at a fairly reliable forecast.

Ways and means are methods of accomplishing an end, and this phrase is sometimes specifically directed to governmental finance and fund raising: the chairman of the Committee of Ways and Means . Means may also be applied to persons and things considered in terms of their past, present for potential usefulness.

• He is the means of our achieving victory; art for art’s sake as opposed to art as a means of spreading propaganda.

Agency suggests causation and implies active intervention. Unlike means , it would not be used of a passive tool employed by others in their action. Instead, it indicates a force, operation or process that on its own produces a certain effect.

• Carbon dioxide is converted into oxygen through the agency of plants; Corruption in government was exposed through the agency of the press.

Applied to persons, agency often indicates a deliberate working or acting on behalf of others: The dispute was resolved through the agency of mediators. An advertising agency , employment agency or travel agency is a business that serves clients, acting in their interests and helping them attain their goals.

Instrumentality is much more formal than the foregoing but is close to means in scope. It focuses on the instrument acting or being used to accomplish someone’s purpose.

• through the instrumentality of a travellers’ aid society, the lost boy was found and returned to his parents.

The term medium has the greatest number of specific senses that relate to the overall concept of means – all stressing the intermediate position of the means . Unlike agency , medium may refer to an intervening substance through which a force may act or in which an effect may be produced.

• Copper is a good medium for the conduction of heat and electricity; Air is a medium of sound.

Medium may also designate a means , technique or vehicle of expression, or the material used for such expression.

• For her, poetry was a congenial medium ; a sculptor whose favourite medium is stone.

In a spiritualistic sense, the word medium denotes a sensitive person, often a woman, who goes into a trance so that spirits may supposedly speak through her, using her as an intermediary for communication with the living. Opposed to this passive mediumship are other senses of the word that refer to a more active intermediary. Here, most commonly, medium is applied to modern channels of communication, often appearing in its plural form media . Radio, television, newspapers and magazines are known as the mass media . Television is an advertising, entertainment and news medium . A modern communications medium in itself – the means, techniques and effects of transmission – may seem to some more interesting and influential than the material or message the medium conveys. In this case, it is no longer a medium in the strict sense of the word, but an end in itself.