These words refer to a position equidistant from the extremities or periphery, or to the vital part of something. Centre , most concretely, indicates such a point within the circumference of a circle or a sphere: the centre of the earth. It can, of course, suggest an approximate location of this sort within any configuration: at the centre of the intersection. Used metaphorically, it suggests a place of extreme density or importance: a metropolitan centre ; at the very centre of his philosophy. Middle , most typically, indicates a point equidistant from the two ends of something: folding the paper down the middle . It can be used more loosely, as an informal substitute for centre, especially when an approximation is intended: right in the middle of the ocean. It is better used for a moment of time than centre : in the middle of the day. It can also indicate a point or moment that occurs in the thick of things: in the middle of our other troubles. Here, it suggests passivity as compared with centre : the man who was at the centre of the controversy. Midst is now mostly used in this last sense of middle but without the implication of passivity; even here it might sound excessively formal except in some standard expressions: in the midst of battle; in the midst of life.

Core specifically suggests the centre of a solid figure: an apple core ; the hollow core of the building. Metaphorically, it has a wide range of uses suggesting the irreducible minimum or quintessence of something that may in its fullness be extensive and manifold: The core of our appeal is freedom of speech; the core of his argument. Heart , at its most concrete, contrasts with all these other words in referring to a vital organ rather than to an exact or approximate centre . In metaphorical uses, however, it may refer to the vital centre of something: the very heart of the city. It may also, like middle, refer approximately to the point of greatest density: in the heart of the jungle. In more abstract uses, it relates most closely to core in suggesting the sine qua non of something, although in this case the irreducible core is also seen as animating principle.

• Magna Carta, signed by King John in 1215 under pressure from his barons, is the heart of British freedom and justice.

Hub , most concretely, refers to the centre of a wheel; in metaphorical uses, it may refer to the psychological centre of a city, even one laid out on a grid system: the hub of business activity in Melbourne. The word seems more exactly used when a network with radiating arms is suggested: the hub of the cocktail party around whom the lesser known spread out in diminishing rank.