Aristotle on Signs
A probablity is not the same as a sign. The former is a generally accepted premise; for that which people know to happen or not to happen, or to be or not to be, usually in a particular way, is a probability: e.g., that the envious are malevolent or that those who are loved are affectionate. A sign, however, means a demonstrative premise which is necessary or generally accepted. That which coexists with something else, or before or after whose happening something else has happened, is a sign of that something's having happened or being. (PrA 70a)
On the middle term:
When three terms are so related to one another that the last is wholly contained in the middle and the middle is wholly contained in or excluded from the first, the extremes must admit of perfect syllogism. By "middle term" I mean that which both is contained in another and contains another in itself, and which is the middle by its position also; and by "extremes" a) that which is contained in another and b) that in which another is contained. For if A is predicated of all B, and B of all C, A must necessarily be predicated of all C. (PrA 25b)
A fallacy called by Aristotle "ek semeiou" (from the sign) is a case of arguing erroneously from the particular to the general e.g. "those who love one another are damaging to the States, since the love of Bill Clinton and Monica Lewinsky damaged the presidency; or that Dionysius is a thief, because he is a rascal; for here again the argument is inconclusive; not every rascal is a thief although every thief is a rascal."
Augustine on Signs
Definition of a sign (Book 2)
A sign is a thing which causes us to think of something beyond the impression the thing itself makes upon the senses.
Thus if we see a track, we think of the animal that made the track; if we see smoke, we know that there is a fire which causes it; if we hear the voice of a living being, we attend to the emotion it expresses; and when a trumpet sounds, a soldier should know whether it is necessary to advance or to retreat, or whether the battle demands some other response. (I.1)Natural Signs
Those are natural which, without any desire or intention of signifying, make us aware of something beyond themselves, like smoke which signifies fire. (I.2)
Conventional Signs
Conventional signs are those which living creatures show to one another for the purpose of conveying, in so far as they are able, the motion of their spirits or something they have sensed or understood… Words have come to be predominant among human beings for signifiying whatever the mind conceives if they wish to communicate it to anyone. (II.3-4)
Literal Signs
[Signs] are called literal when they are used to designate those things on account of which they are instituted. [E.g. ox to signify a herd animal] (X.15)
Figurative Signs
Figurative signs occur when that thing which we designate by a literal sign is used to signify something else. [E.g. ox where the word signifies the animal but the animal signifies something else, namely an evangelist (Deut 25:4; 1Cor 9:9; 1Tim 5:18)] (X.15)
The Causes of Misunderstanding and Their Remedies
Unknown Literal Signs
Against unknown literal signs the sovereign remedy is knowledge of languages [E.g. untranslatable words; words ambiguous in the original so that more than one translation is possible; unknown words and expressions in one’s own language] (XI.16-XV.22)
Unknown Figurative Signs
Among figurative signs, if any impede the reader, he should study them partly with reference to a knowledge of languages [e.g. the meaning of untranslated symbolic names, such as Adam ("man")] and partly with reference to a knowledge of things. … An ignorance of things makes figurative expressions obscure when we are ignorant of the natures of … things which are often used in the Scriptures for purposes of constructing similitudes [E.g. animals, plants, herbs, numbers, music] (XVI.23-XVII.27)
Ambiguous Literal Signs (Book 3)
When words used literally cause ambiguity in Scripture, we must first determine whether we have mispunctuated or misconstrued … When investigation reveals an uncertainty as to hos a locution should be pointed or construed, the rule of faith should be consulted … But if both meanings, or all of them, in the event that there are several, remain ambiguous after the faith has been consulted, then it is necessary to examine the context of the preceding and following parts surrounding the ambiguous place, so that we may determine which of the meanings among those which suggest themselves it would allow to be consistent. (II.2)
Ambiguous Figurative Signs
Against Taking Figurative Signs Literally
At the outset you must be very careful lest you take figurative signs literally. … There is a miserable servitude of the spirit in this habit of taking signs for things, so that one is not able to raise the eye of the mind above things that are corporal and created, to drink in eternal light. … He is a slave to a sign who uses or worships a significant thing without knowing what it signifies. But he who uses or venerates a useful sign divinely instituted whose signifying force he understands does not venerate what he sees and what passes away but rather that to which all such things are to be referred (V.9, IX.13).
Distinguishing between Literal and Figurative Signs
To this warning that we must beware not to take figurative or transferred expressions as though they were literal, a further warning must be added lest we wish to take literal expressions as though they were figurative. … Whatever appears in the divine word that does not literally pertain to virtuous behavior or to the truth of faith you must take to be figurative. … Scripture teaches nothing but charity, nor condemns anything but cupidity, and in this way shapes the minds of human beings. … Therefore in the consideration of figurative expressions a rule such as this will serve, that what is read should be subjected to diligent scrutiny until an interpretation contributing to the reign of charity is produced. If this result appears literally in the text, the expression being considered is not figurative. (X.14-15, XV.23)