Full Idea
Definitions of things which may be understood to have some cause, must consist of such names as express the cause or manner of their generation, as when we define a circle to be a figure made by the circumduction of a straight line in a plane etc.
Gist of Idea
Definitions of things that are caused must express their manner of generation
Source
Thomas Hobbes (De Corpore (Elements, First Section) [1655], 1.6.13)
Book Reference
Hobbes,Thomas: 'Metaphysical Writings', ed/tr. Calkins,Mary Whiton [Open Court 1905], p.32
A Reaction
His account of the circle is based on its mode of construction, which is the preferred account of Euclid, rather than a statement of its pure nature.