These words all refer to something upon which something else rests or depends. Basis differs from base in being more often used in metaphorical senses: The basis of his argument was that the victory was unattainable without seriously jeopardizing domestic programmes. Base , on the other hand, normally refers to physical objects that form the lowest or supporting part of anything: the base of a statue. It can be used metaphorically as well: the base of a theory. In this sense basis and base are practically synonymous; base , however, more often suggests the idea of an underlying foundation, whereas basis is broader in application and may suggest the idea of a central or fundamental part s well as that of an underlying principle.

• Axioms are the base of geometry; The basis of his decision; One what basis do you propose to pay me?

Foundation can mean the base on which something rests: the foundation of a building. Foundation suggests a more imposing, solid structure than base , which can apply to the bottom part of anything: the base of a lamp; the foundation of an ancient city. Foundation also means that on which anything is founded, and in this sense is close to basis : The foundation of democracy is the will of the people to preserve liberty. It should perhaps be noted that foundation is now used commercially to refer to a variety support, such as facial make-up applied beneath other make-up and certain undergarments that hold in vital parts of the body so that outer-garments do not reveal their actual shape.

Ground , as here considered, means a foundation or basis for a decision, argument or relationship. It often used in the plural, it may be construed as singular.

• The grounds for his decision was never clearly stated; Absenteeism constitutes grounds for dismissal.

Grounds implies the underpinnings of reason: Leverrier’s mathematical computations were the grounds for his theory that there was a planet beyond Uranus.