'agent' vs 'agency'

Question

What are the similarities and differences? I already know about (and therefore am not asking about) a reserved number of definitions unique to each noun, but what about the following definitions that look alike?

agency = 1. [often with adjective or noun modifier] A business or organization providing a particular service on behalf of another business, person, or group

= 2. [mass noun] Action or intervention producing a particular effect

agent = 1.2. A person or company that provides a particular service

2. A person or thing that takes an active role or produces a specified effect:

Answer 1

At the most abstract level:

Agent = he who or that which acts to produce an effect or result.

Agency = the action(s) / performance of the agent to produce an effect or result.

A company can be an agent because a company or organization can be understood in figurative terms as an actor ; it has entity status even though it is intangible, a group or association of individuals.

When the company is conceptualized in terms of its efficacy, the things it performs, it is said to be "an agency"; and so the noun agency comes to stand for a company engaged in a particular business.

Answer 2

Agent in the sense "A person or company that provides a particular service" chiefly denotes a person; it denotes a company only by extension. By contrast, agency in the sense "A business or organization providing a particular service on behalf of another business, person, or group" never denotes an individual. Therefore, expressions of the form "___ agent" and "___ agency" often come in pairs, with "___ agent" denoting an individual and "___ agency" denoting a business. (Examples include "travel agent/agency" and "talent agent/agency".)

Agent in the sense "A person or thing that takes an active role or produces a specified effect" denotes the cause; for example, yeast is a "leavening agent" because it causes bread to leaven. By contrast, agency in the sense "Action or intervention producing a particular effect" denotes the causation; one could write of "the agency of the yeast" (though it would sound very old-fashioned).