Following up on the explanation of the interpretant given in his 1909 letter to William James, Peirce is careful to distinguish between the two kinds of prior knowledge needed by the interpreter: knowledge of the sign’s object, and knowledge of the sign-system.
All that part of the understanding of the Sign which the Interpreting Mind has needed collateral observation for is outside the Interpretant. I do not mean by “collateral observation” acquaintance with the system of signs. What is so gathered is not COLLATERAL. It is on the contrary the prerequisite for getting any idea signified by the sign. But by collateral observation, I mean previous acquaintance with what the sign denotes. Thus if the Sign be the sentence “Hamlet was mad,” to understand what this means one must know that men are sometimes in that strange state; one must have seen madmen or read about them; and it will be all the better if one specifically knows (and need not be driven to presume) what Shakespeare’s notion of insanity was. All that is collateral observation and is no part of the Interpretant. But to put together the different subjects as the sign represents them as related,—that is the main of the Interpretant-forming.
EP2:493-4 (1909)
As a matter of fact, Shakespeare’s Hamlet exists as a play as long as performances occur in theatres, recordings or memories, or copies of the text exist in print. It is also a fact that Hamlet is Prince of Denmark in the fictional universe of that play. Whether any of the events in that play took place in the past is irrelevant to those facts. Strictly speaking, a fiction can neither tell the truth nor lie about what actually happened in the past, because the historical universe is not the object of that sign. Yet a fiction can sometimes have a greater effect on the future of the real world than many a factual text; and that effect is due to the real power of symbols as legisigns to determine actual events as dynamic interpretants.
The same is true of scriptures, although those who read them as scriptures do not usually think of them as fictions. What kind of collateral observation does it take to acquaint us with what is denoted by an expression like “the Will of God,” or divine “judgment” as to what is right or wrong? We have collateral experience of ourselves willing and judging, and we know that our own intentions and judgments (including perceptual judgments) are constrained by the form of our embodiment. If those constraints do not apply to God, what collateral observation could acquaint us with what is denoted by an expression like “the Will of God”? The religious interpreter of such a Sign is indeed driven to presume what God’s notions of good and bad are (or in a different religious context, what “enlightenment” is like for a buddha).
This kind of presumption, which is essentially what we call faith, can only be invested in an imaginative creation which is a symbol very like a metaphor. Its interpretant is the religious practice of the interpreter, formed by putting together ‘the different subjects as the sign represents them as related.’ (Or ‘the different objects,’ since Peirce remarks in the same place that ‘Subject and Object are the same thing except for trifling distinctions.’) These objects, together with their relations, often constitute ‘the environing universe’ (EP2:341) in which that practice is performed.
We know the meaning of the Sign only by its fruits in practice. These are determined, at least partially, by the interpreter’s presumptions about the creator’s intentions; but those presumptions, along with any collateral observations furnishing the believer’s acquaintance with the Objects, are ‘outside the Interpretant.’ Our understanding of the Sign’s meaning therefore depends, more crucially than usual, on our ‘acquaintance with the system of signs’ inside the Interpretant – which is, in practice, inseparable from the interpreter’s guidance system. That too we know by its fruits, not by its presumptions – and certainly not by our own presumptions.