A natural sign is a perceptual datum, an actual material fact or item, materially linked, necessarily or ambiguously, to another fact or item or state of things not perceptually accessible.
A natural sign is typically an indisputable fact, “as certainties, we have, in the first place, what is perceived by the senses, as what we see, what we hear, as signs [signa] or indications” (Quintilian, V, 10, 12).
A natural sign is quite different from a linguistic sign, for which the link between signifier and signified is social and arbitrary. It is not a global analogon of the thing it “represents”, as in the case of analogical thinking. Nor is it a symbolic representation of the associated phenomenon.
The natural sign is just a part of the phenomenon through which the observer can access the whole phenomenon. The link between the present natural sign and its absent counterpart can be:
The very first manifestation of a phenomenon: a red setting sun / rainy weather tomorrow
A remnant of something disappeared: the leftover / the meal
A part of a whole: a hair / a person
An effect to its cause: being tired / having worked
1. Natural signs, clues and traces
Clue is an accurate synonym of material sign, since to look for clues, one must necessarily have to deal with some “intricate procedure or maze of difficulties”, or be seeking “to find something, understand something, or solve a mystery or puzzle” (MW, Clue). These description fit well with exploratory argumentative situations. Generally speaking, an argument is indeed a clue to a conclusion; etymologically, a clue is ‘a ball of thread’; hence, one used to guide a person out of a labyrinth” (OD, Clue). Clues are typically looked for “in the detection of a crime”; “police officers are still searching for clues” (ibid.). Yet clue is also used to refer to a “piece of information” given to someone; and this is not a natural sign in the sense discussed in this entry.
Traces, such as fingerprints (necessary sign), or tire marks (probable sign), are a special kind of natural signs, but, insofar traces are leftovers, “a mark […] left by something that has passed”, not all material signs are traces; smoke is not a trace of fire, whereas ashes are.
Index, indication, indicator can also be used with the meaning of “natural sign”.
2. Reasoning on probable and necessary signs
The relation of the natural sign to its counterpart is inferential in nature:
Anything that when it is, another thing is, or when it has come into being the other has come into being before or after, is a sign of the other’s being or having come into being.
(Aristotle, P. A., II, 27; my italics for the sign and underlining for the counterpart).
These inferences are exploited in concrete argumentations such as:
I can see smoke, the house is on fire
Peter’s face is flushed, he must have a fever
The quality of the argumentation depends on the nature of the link it exploits. If the sign is necessary, the argumentation is conclusive; if it is probable, the possible claim is slightly more probable that it would be in the absence of the argument; probable signs reduce uncertainty, S. Abduction.
Probable signs are distinct from human and social probabilities.
— A necessary sign (tekmerion) is associated with a material being or state of affairs. It corresponds to a material, empirical necessity (not a logical necessity):
A scar, an ancient wound
Callous hands, being a manual worker
Footprints on the sand, humans on the island
Such signs thus have the force of proof, the associated syllogism is valid, as in the following propter quid argument, S. A priori
Law (major): A woman who has milk has given birth (if M, then B)
Sign (minor): This woman has milk.
Conclusion: This woman has given birth.
— Probable (contingent) signs (semeion) may correspond to several associated realities. Contingent signs are ambiguous, whereas necessary signs are unambiguous
tiredness is a possible sign of having worked
being flushed is a possible symptom of having a fever
Typically, peripheral indicators are non-necessary signs: “he has a guilty look so he feels guilty, so he is guilty”, S. Circumstances. The associated syllogism is not valid:
Law: Women who have given birth are pale.
Sign: This woman is pale.
Conclusion: This woman has given birth.
A necessary condition is taken for sufficient: one might simply have a naturally pale complexion, or one might be pale because one is ill. The probable sign brings only one piece of evidence (judicial); it can support a suspicion, it is not a proof.
The human body is an inexhaustible source of natural signs; white hair and flexibility of the skin are natural signs indicative of age and the global physical condition of the person. In medicine, co-occurring non-necessary signs are grouped in a syndrome, that is to say “a group of signs and symptoms that occur together and characterize a particular abnormality or condition.” (MW, Syndrome). For example, the Samter’s syndrome
Samter’s Triad or Aspirin Sensitive Asthma, is a chronic medical condition that consists of asthma, recurrent sinus disease with nasal polyps, and a sensitivity to aspirin and other non-steroidal anti-inflammatory drugs (NSAIDs).
This grouping of signs is the basis of conclusive medical reasoning: if a patient suffers from asthma and is sensitive to aspirin, then he would very probably also has a problem with nasal polyps. He should be checked for this third condition.
When grouped, a series of separately non-conclusive signs might constitute a body of conclusive evidence. An area of the body may be red, because it has been rubbed; hot, because of incipient sunburn; painful or swollen because of an accidental blow. But if it is at once red, painful, hot and swollen, then, we can say that it is inflamed, S. Convergent argumentation.
To guess the intentions of the enemy, the soldier observes their acts and movements and then reasons from a cluster of converging signs:
The writer Roland Dorgelès had “the singular privilege of baptizing a war”, as “the Phony War”, which refers to the strangely calm situation on the front between September 3rd 1939, the date of the declaration of war, and May 10th 1940, the date of the invasion of Belgium, the Netherlands, Luxembourg and France by Nazi Germany. His book, The Phony War, brings together a series of reports on the front during this period. In April 1940 he was in Alsace, at an observation post.
Seen from above, it looks as though the enemy lines are dominated as if from a balcony. […] The sergeant who never loses sight of them, now knows their habits, knows where they come from and where they go.
‘There, he points out, they are digging a sap. Look at the stirred earth… This gray house has certainly been consolidated… look at the embrasures… And those tiles over there? Their workers at this moment are mainly occupied there. This morning I counted sixty of them, returning from the building site, with lamps: so they must be digging underground.’
From dawn to darkness, our watchmen remain leaning over the telescope.
Roland Dorgelès, [The Phony War], 1957
The whole art of Sherlock Holmes resides in the observation, interpretation and combination of clues, S. Deduction. The clue is a trace of the action from which a modus operandi can be inferred. If the window panes have been shattered into pieces, and these are found lying inside the drawers which have been torn from the cupboards and thrown onto the room, then we can be sure that the room was first ransacked and the windows were then fractured to give the false impression that the window had been broken to enable entry into the room. So, they entered the room through the door; so they had a key. Who has the keys?
Certain individuals exploit and investigate clues is a professional capacity. Sign-based arguments are field-dependent. On the basis of a clue, the detective knows how to reconstruct the scenario of a crime; the historian knows how to judge the authenticity of a document; the archeologist knows how to reconstruct the city map, the paleontologist knows how to determine the age of the skeleton (Ginzburg 1999). The informed reasoning of these professionals should be considered to be exemplary of practice-oriented argumentation studies.