These words refer to the gradual gaining of ground by something. Spread is the most informal and general of these, with particular usefulness in referring to the ground gained by a species, a disease, an idea or a cultural mannerism: deciduous trees that slowly spread over most of the world; rats that spread bubonic plague throughout Europe; a rash spreading over most of her body; ideas that spread more rapidly in an age of instant communications; Carnaby Street fashions that spread quickly from London to Australia. Propagate also refers to something that gains ground or adherents. It suggests a conscious, laborious effort to stimulate the healthy growth of something: propagating a new species of seedless grapefruit. It can apply also to an insidious or harmful spreading of information: propagating the myth of racial superiority for his own devious ends.

Distribute and circulate lack both the negative implications possible for propagate . They are both most often neutral in their concentration on techniques for the wide spreading of something through space. Distribute emphasizes easy access and is particularly relevant in reference to periodicals: paper vans that distribute the day’s newspapers throughout the city. The point of the word may be the availability of something to everyone concerned or the parcelling out of a given quantity among a group: distributing a copy of the new health-insurance plan to everyone in the office. Circulate is less concrete in reference than distribute . It, too, may refer to distributing periodicals

• a paper that is circulated to the whole metropolitan area

But more often this word, as a verb, refers to actual movement through a mass: arterial blood that circulates oxygen throughout the body. The word may point also to a movement of ideas or mannerisms among a circle of people: conservative notions that circulate among the company’s power elite.