The third characteristic of the statement is that it always brings a collateral space into operation. We cannot consider the enunciative function in a sentence without considering various other domains; or at least, we could only speculate as to the possible nature of that particular enunciative function. The statement is not a statement in isolation. The sentence and the proposition, however, are. Although they refer outside themselves, they remain perfect sentences or propositions even in isolation. 'A statement [on the other hand] always has borders peopled by other statements.' This is not, however, the same thing as 'context' in its usual sense, for two reasons: first, the enunciative formation extends beyond the group of contextual factors that motivate a given statement; and second, this formation does not concern the psychological factors that are usually part of context. In short, the 'associated field' of the statement is more extensive than the motivational 'context' we are used to. The associated field (or 'enunciative field') of a given statement, then, is made up primarily of other statements, both actual and possible. It includes the series of statements of which the statement in question is an element; all the statements to which the given statement refers by adaptation, opposition, commentary, and so on ('there can be no statement that does not reactualize others'); all the formulations that the statement makes possible; and all the formulations that share the statement's 'status' (its authority, its irrelevance, and so on). This associated field is what makes a series of signs a statement.
Fourth and finally, the statement has to have a material existence. In fact, it cannot exist without one: the statement is 'partly made up of this materiality' in that material existence gives us the crucial 'coordinates' of a statement, its role in a spoken conversation, a novel, a legal brief, etc. Statements have a very specific kind of materiality, different both from sentences or propositions and from enunciations. Enunciations occur whenever 'a group of signs is emitted,' and therefore each enunciation is unique. If we consider an enunciation simply as a propositional sentence, however, we find that it is identical with any of its repetitions (since we are only considering its content, not the conditions of its emission). The statement falls somewhere in- between. In some cases, we can identify a single statement even when there are multiple enunciations of it (as in, say, a group prayer). Yet in other cases, two enunciations that share the same content, form, rules of construction, and intention must still be seen as distinct statements if their associated fields differ.
The materiality proper to the statement, unlike the materiality of the enunciation, involves more than just the particular physical material that carries the statement. Generally, two copies (or even editions) of the same book contain identical statements, even though their materiality may vary widely; in fact, this identity of different material statements is part of what is guaranteed by the authority of the 'book.' On the other hand, a posthumous edition of a book may not have the same value to a literary historian as an edition published in the author's lifetime. In short, the materiality of the statement comes into play at the level of material institutions like the book or the contract, rather than the level of simple material objects or sounds.
The aim here is not to come up with criteria by which statements can be individuated; we are not concerned with finding a stable unit for the statement (as there is in the case of the sentence). The unit of the statement is highly variable, even for the same text. In a large-scale history, for example, two texts could be seen as a making a single statement in support of theory of Darwinian evolution. In a close study of the history of that theory, however, the two texts would no doubt be found to be different statements (one Darwinian, one neo-Darwinian). Thus, the identity of a statement also depends on this 'field of use.'
In sum, then, the statement has a peculiar kind of 'repeatable materiality' that distinguishes it from linguistic signs on the one hand and material signs on the other. Because the enunciative function of the statement lies in the middle ground between these two restricted aspects of language, it allows us to see a new kind of history, a history whose basic element is that of the statement: 'The statement circulates, is used, disappears, allows or prevents the realization of a desire, serves or resists various interests, participates in challenge and struggle, and becomes a theme of appropriation or rivalry.'
Foucault gives four major factors that distinguish the statement from other aspects of signs. In thinking about these factors, it generally helps to consider the statement less as a thing than as a unique method for the analysis of sets of signs. In places, Foucault uses the term 'repeatable materiality' as a catchall term for these four factors. The phrase is a kind of paradox: if a set of signs gains its identity solely on the basis of its material existence, it cannot be repeated (since this would involve new material); if, on the other hand, a set of signs gains its identity solely through non-material factors like grammar or propositional content, it can be repeated ad infinitum (since signs, in and of themselves, retain their identity across various material instantiations).