Arguments are lines of reasoning using
propositions (claims or assertions)
Propositions come in 3 forms: factual
claims, opinions and ideas (including
hypotheses and theories)
Examples of Arguments
You shouldn’t hit people, Johnny. Hitting hurts people,
and it’s wrong to hurt people.
My client was at the bar when the murder occurred.
Several eyewitnesses have reported seeing him there,
and his receipt indicates that he didn’t leave until after
the murder occurred. Thus, he could not have
committed the murder
If the Cubs want to start winning, they need to redesign
their uniforms. This always seems to give teams a new,
winning attitude. You know, kind of a break from the
losing days of the past.
Bill cheated on you once before; he’ll do it again. Men
like that just don’t change.
2 Key Distinctions
Strong v. Persuasive arguments: Arguments are
strong (or cogent) if they are well reasoned;
arguments are persuasive if they succeed in
convincing. Strong arguments are not
necessarily persuasive; persuasive arguments
are not necessarily strong.
Descriptions v. Inferences: Descriptions are
reports; inferences are conclusions from or
interpretations of those reports.
Many arguments contain assumptions or
missing premises—i.e., incomplete
presentations of the argument.
Assumptions can be warranted or
When are assumptions warranted?
Readily available evidence
Factual claim shared with target audience
Value claim shared with target audience
When are assumptions
Based on speculation
Based on evidence not readily available
Disagreement over factual matters
Disagreement over value judgments
It’s wrong to spank your children because
We should put tighter restrictions on
divorce. As Jesus told us, “What God has
joined, let no man sunder”.
Jim wouldn’t have developed lung cancer
if he had quit smoking.
It was wrong of us to go to war in Iraq,
because it’s killing innocent people.
Types of Evidence I
Speculation or Opinion
All these are evaluated by abductive
methods—by Inference to the Best
Types of Evidence II
Evaluated by: observation
Types of Evidence III
Evaluated by empirical observation and
Types of Evidence IV
Value claims (incl. taste, aesthetic judgment,
Analogies (including Precedents)
Evaluated by coherence, relevance and
Some arguments have preliminary
conclusions as steps toward a major
Some arguments provide evidential
support for their premises
^ These are called Lemmas
An Example: William Lane Craig’s
P1: Everything that begins to exist has a cause
P2: The Universe began to exist
L1: Big Bang Cosmology
L2: The logical impossibility of an actual infinite
PC1: Therefore, the Universe began to exist
P3: Nothing can cause itself to exist
PC2: Therefore, something else caused the Universe to
P4: The only plausible cause for the Universe is God
L3: Because God is omnipotent and omniscient
C: God caused the Universe to exist