Diagramming Arguments
Congruent and Linked
Arguments

An Argument
• An argument = a set of
statements connected by a
special relationship of
justification; the
statements provide
evidence for the main claim

Independent Premises
• Falsity of one doesn’t cancel
support the other provides.-
independent proof.
• You shouldn’t buy a T.V. that
costs over $300. This costs
$450. It is also too big for your
room. Don’t buy this T.V.

Dependent Premises
• Falsity of one can cancel
support for others-
interconnected.
• These premises cannot stand
alone to provide proof.

Example of Dependent
• No floor with 2x4 joists on
two foot centers is strong
enough. This floor has 2x4
joists on two foot centers.
So, this floor is not strong
enough.

Convergent Arguments
• In convergent arguments,
the premises provide
different and independent
reasons for the claim.
Each can support the claim
by itself.

Example-Convergent
• Nuclear power plants should
not be built, because they are
dangerous. And, the power
from these plants is not
essential. Finally, these
plants are not fair to future
generations.

Linked Arguments
• Linked argument- one in which
the reasons are dependent on
one another for their strength.
They cannot stand alone.

Linked Argument
• There is reason to think the
suspect is linked to this
crime. The shots were fired
from a jaguar; jaguars are not
usual to this area; and the
suspect owns a white jaguar.

Argument Diagramming
• Identify each claim and
number them.
• Provide missing parts if
needed.
• Determine relation of
claims and diagram.

Persuade or Argue?
• Arguments seek to prove a
point; to establish truth of a
claim on basis of other claims.
• Persuasion seeks to win
others to a point of view- may
or may not have proof.

Is this an argument?
• “The desperate attempt by
Hawks to link Iraq to the
war on terrorism is based
on blatant mis-information.
• Is there evidence?

Enthymemes-assumptions
• There can be implied or
missing parts of an
argument. Often it is
assumed that you will
supply the missing
information or think it
automatically.

What is missing?
• Jones will not win the
election since his District
is Democratic.
• You should prefer this tea
as do professional tea-
tasters.

What is missing?
• This film is too intellectual
and thus probably will not be
economically successful.
• Being a barber, you are no
doubt a good
conversationalist.

Common Assumptions
• Alice could not have been
the robber, since Alice was
not in Key West when the
crime was committed/ At
10 a.m., August 9, she as in
Miami.

Dubious Assumptions
• The Anacin difference-two
standard aspirin tablets
can 650 milligrams while
two Anacin tablets contain
800 milligrams.- better?