“Judging a book by
Assumes one thing or event is a reliable
indicator of another thing or event
the presence of one thing signifies the
other, but does not cause the other.
a flag at half mast
signs can be:
status symbols, economic indicators,
political actions, physiological symptoms,
or other indices.
effect-to-cause reasoning is one form of sign
example: an MD relies on symptoms
(fever, sore throat) to make a preliminary
examples of sign reasoning
• “It has been 50,000 miles since your car was last
serviced. You need a major tune-up.”
• “That guy‟s pants are „saggin‟ and he‟s wearing a
Raiders jacket, so I‟ll bet he‟s a gang member.”
• “The last two times I ate at Coco‟s, the same
waitress took my order. I think she digs me.”
• “Naomi didn‟t pick up when I called her, so I guess
she‟s not home.”
illustration of sign
Grounds: leaves are
Claim: Winter is falling, birds are
approaching flying south,
associated with the
advent of Winter
real-life examples of sign
• Signs your significant other is fooling around
• Warning signs of suicide.
• Signs that Iran is seeking nuclear weapons rather
than commercial nuclear technology.
• Does the location of U.S. aircraft carriers signal the
likelihood of military action?
• Do economic signs suggest the economy has hit
• inferring things about a person‟s values or lifestyle
from the person‟s appearance.
Al Gore uses sign reasoning to
prove global warming is occurring
• Gore cites
evidence, such as the
fact that the warmest
years on record have
all occurred since
1990, as evidence of
• Melting glaciers and
more severe hurricanes
are signs of warming
a sign that it is time to
replace your tires
• place a US penny into a
groove between tread, with
Lincoln's head down. If the
tread is at or beyond the top
of Lincoln's head you have at
least 3/32-inch of tread left, a
• if you can see above
Lincoln's head or any of the
"In God We Trust" letters
above his head, then you are
ready for a new tire.
Poker tells: can you tell a player’s
hand from nonverbal cues?
• Glancing at chips: “if a player
immediately glances down at his chips
as soon as he sees his cards, it almost
always means that a player's hole cards
are strong (from AskMen.com)
• Sitting up straight, leaning forward:
A player who has been slouching
suddenly seems to take interest in the
game and leans forward is usually
holding a strong hand (from
• Splashy bet: If a player makes a large
bet by throwing his chips into the pot in
a grand, exaggerated fashion, he is
trying to bluff you out of the pot (from
You are what you own: Material
goods as status symbols
• Consumption and materialism often
function as status symbols in
• Rolex watches, Tiffany jewelry
• Hummers and other luxury cars
as urban status symbols
• “trophy” wives
• designer clothing (Armani,
• state of the art technology
(plasma TVs, wireless laptops,
GPS devices, cell-phones,
• platinum credit cards
• membership in country clubs
signs of steroid use and
• If an athlete bulks up
suddenly, is it a sign he
is on steroids?
• If an actress loses
weight is it a sign she
has an eating disorder?
Is the purple Teletubby gay?
• The Rev. Jerry Falwell charged
that Tinky Winky was gay because
“He is purple -- the gay-pride
color; and his antenna is shaped
like a triangle -- the gay-pride
handwriting analysis as sign
• Handwriting experts analyzed the
letters containing anthrax for clues
about their sender
“Circumstantial evidence” is
based on sign reasoning
• Circumstantial evidence: inferring • Sherlock Holmes in
one fact from another. the Boscombe Valley
• Direct evidence: a witness Mystery:
testifies that he saw a "Circumstantial
defendant shoot a person, and evidence is a very
the person subsequently died tricky thing. It may
of a gunshot wound. The seem to point very
witness would be providing straight to one thing,
direct evidence of a material but if you shift your
fact in the case. own point of view a
• Indirect evidence little, you may find it
(circumstantial): a witness pointing in an equally
testifies that he heard a shot uncompromising
and when he arrived on the manner to something
scene he saw the defendant entirely different."
standing over the body with a
smoking gun in his hand.
• Laci Peterson's body
washed up a few miles away
from where Scott Peterson
said he was fishing alone
• He returned to the location
three more times before her
body was discovered.
• Could it be just a
increased “chatter”: as a sign of
• May 20, 2003: Homeland Security
Secretary Tom Ridge said there is
no "credible, specific information"
about targets or method of attack,
but he says increased “chatter”
suggests attacks on U.S. soil may
applications of sign reasoning
• in business: economic indicators, inflation rate,
consumer confidence, housing starts, unemployment
• in advertising: associating products with status,
• in medicine: symptoms, fever, dizziness, blood
• in religion: 666, biblical signs of the apocalypse
• in law: circumstantial evidence
• in tabloids: if two celebrities are seen together, it is
taken as a sign they are having an affair, or if they
are not seen together it is taken as a sign of a
fallible versus infallible signs
• fallible: nonverbal correlates of deception.
• fallible: Where there is smoke, there is fire.
• infallible: genetic markers as proof of identity.
• infallible: a shadow signifies the presence of a physical body
• Note: infallible signs are much more common in the
tests of sign reasoning
• Does one fact or event allow one to reasonably infer
another fact or event?
• How reliable or consistent is the sign?
• Is the sign fallible or infallible?
• Is the sign ambiguous (could it signify something else?)
• Is the sign relevant (could it signify nothing?)
• Are there a sufficient number of signs?
• Are there negative or contradictory signs?