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– Theory of knowledge: the branch of philosophy
that studies the nature of knowledge, in particular
its foundations, scope, and validity.
– Theory of reasoning: the branch of philosophy
that deals with the theory of deductive and
inductive arguments and aims to distinguish good
from bad reasoning.
From Bing Dictionary
“Don’t neglect your critical faculties. Remember that God is a rational God,
who has made us in His own image. God invites and expects us to explore His
double revelation, in nature and Scripture, with the minds He has given us,
and to go on in development of a Christian mind to apply His marvelous
revealed truth to every aspect of the modern and post-modern world.” – John
Logic: “Logic is the study of right reason.… That is the main point. Logic is a
study, an ordering, of how to think rightly, or how to find truth. Paraphrasing
this, we might say, logic is a way to think so that we come to correct
conclusions.” - Geisler and Brooks, Come, Let Us Reason, An Introduction to
Logical Thinking p. 13
Is It Futile?
• Some people site 1 Corinthians 1-2 to say
human reasoning and argumentation are
• However, Paul later in the epistle supports
argumentation and reasoning.
– See 1 Corinthians 15 and examples of Paul in Acts.
1 Corinthians 1-2 & Colossians 2:8
• “What is in view here is the prideful use of
reason not reason itself.” – J. P. Moreland
• In addition, Paul’s comments may be directed
at the sophists of the time who valued
persuasion over logic.
– For the sophist it was more important to win a
debate than to come to true conclusions.
“Scripture and right reason were considered twin
allies to be prized and used be disciples of Jesus.”
“Knowledge is the fruit of study, and knowledge is
necessary for wisdom.”
“The word logos means ‘evidence or argument
which provides rational justification for some belief.’”
- J. P. Moreland, Love Your God With All Your
• “Some argue that the human intellect is
fallen, depraved, darkened, and blinded, and
therefore human reason is irrelevant or even
suspect when it comes to becoming or
growing as a Christian.” - J. P. Moreland
• “Total depravity means that the entire person,
including the intellect, has been adversely
affected by the Fall and is separate from God.”
- J. P. Moreland
Total depravity does not mean we should not nor
cannot use reasoning skills as anti-intellectuals claim.
Total depravity properly understood means that we
cannot save ourselves. In Romans 1 Paul tells us we
are without excuse because by reason we know there
is a God. God has given humans a gift that no other in
the animal kingdom has, mainly an intellect, the ability
to reason. We are held accountable before God with
what reasoning powers we have. It would be a shame,
no a sin, to not use the gifts God has given us to their
full potential. Our sinful state mares our
understanding, it does not eliminate it.
• Three aspects of Biblical faith
– Notitia (knowledge)
– Fiducuia (trust)
– Assensus (assent)
“God is not honored when His people use bad arguments for
what actually may be correct conclusions.”
“A confident mind is a mind free to follow the truth wherever
it leads, without the distracting fear and anxiety that comes
from the attitude that maybe we’re better off not knowing
the truth. This is one reason why Christians need not fear
the honest examination of their faith.”
- J. P. Moreland, Love Your God With All Your Mind
“We can’t avoid reasoning; we can only avoid doing it well.”
- Kreeft and Tacelli, Pocket Handbook of Christian
“Our God is a God of truth, reason and logic.”
- Moreland, Love Your God With All Your Mind 113
“Our Lord is a God of reason as well as of revelation.”
- Moreland, Love Your God With All Your Mind 43
• Necessarily false:
– Cannot be true in anyway.
– Not clearly expressed or well thought out, and
consequently difficult to understand.
– Statements that are necessarily have opposite
meanings or opposite truth values.
– Some people are moral. No people are moral.
– Some people cannot be moral if all people are not
– The both cannot be true, at least on is false and
both could be false.
– All cars are black. No cars are black.
– One must be false they both cannot be true but
they both could be false as in this example.
– Switching the subject and the predicate.
– All Fords are cars. All cars are Fords.
– Some Fords are cars. Some cars are Fords.
Law of Identity
• It states that an object is the same as itself: A →
A (if you have A, then you have A).
– “This illustration can be generalized into a truth about
the nature of identity: For any x and y, if x and y are
identical (they are really the same thing, there is only
one thing you are talking about, not two), then any
truth that applies to x will applies to x will apply to y
and vice versa. This suggests a test for identity: if you
could find one thing true of x not true of y, or vice
versa, then x cannot be identical to (be the same thing
as) y.” J.P. Moreland
Law of Noncontradiction
• Self-refutation is a statement that cannot satisfy
its own standard.
• The statement refers to itself and fails to satisfy
its own criteria.
• Ask yourself, “Does the claim apply to itself?”
– “All English sentences are false.”
– “There is no truth.”
– “There are no absolutes.”
– “I do not exist.”
Law of Excluded Middle
• It states that for any proposition, either that
proposition is true, or its negation is.
– Socrates is mortal.
– Mortality has only two states, mortal or immortal.
– There is no state of partial mortality (no middle
– Either Socrates is mortal, or it is not the case that
Socrates is mortal.
• Premise, a proposition that forms the basis of
an argument or from which a conclusion is
drawn (Encarta World English Dictionary).
• Conclusion, a decision made or an opinion
formed after considering the relevant facts or
evidence (Encarta World English Dictionary).
• Deductive arguments are either valid or
invalid. If the premises are true it follows the
conclusion must be true. A valid argument is
a sound argument.
• Inductive arguments don’t guarantee that the
premises validate the conclusion, however
they supply support for the conclusion.
– Probability not certainty.
– Facts are determined by repeated observations.
• A syllogism is a deductive argument that
consists of exactly two premises and a
– Major premise: All mammals are warm-blooded.
– Minor premise: All black dogs are mammals.
– Conclusion: Therefore, all black dogs are warm-
• A string of any number of propositions forming
together a sequence of syllogisms such that the
conclusion of each syllogism, together with the
next proposition, is a premise for the next, and so
– It is raining.
– If we go out while it is raining we will get wet.
– If we get wet, we will get cold.
– Therefore, if we go out we will get cold.
• The validity of an argument does not depend
on the actual truth or falsity of its premises
• The validity of an argument depends solely on
whether or not the argument has a valid
• A sound argument is a valid argument with
• A sound argument, being both valid and
having true premises, must have a true
Burden of Proof
• What level of proof is sought?
– Absolute certainty
– Beyond reasonable doubt
– Preponderance of evidence
– Clear and convincing
• Something is certain only if no skepticism can
Burden of Proof
• Semper necessitas probandi incumbit ei qui
• The necessity of proof always lies with the
person who lays charges.
Evaluating Evidence and Claims
• Three Questions:
– Is it possible? Is it even remotely possible?
– Is it plausible? Is it logically consistent? Is it
– Is it probable? Is it the best explanation given all
“…examining [arguments] can help us to see how subtle but misleading
arguments can be untwisted through careful reading and good thinking.” -
“You follow the evidence of what you can see to conclude the existence of
something you cannot see. The effect needs a cause adequate to explain it.”
- Greg Koukl
“…when we use our reason and base our decisions on the best assessment
of the evidence we can make, we increase our chances that our decisions
are based on true beliefs.” J. P. Moreland
“Taking the roof off” assume for the sake of argument their idea or premise
then take that premise and put it to the practical test and see where it goes.
“It forces people to ask if they can really live with the kind of world they are
affirming.” - Greg Koukl
• An informal fallacy is an argument whose
stated premises fail to support their proposed
• The deviation in an informal fallacy often
stems from a flaw in the path of reasoning
that links the premises to the conclusion.
• Informal fallacies do not necessarily mean the
conclusions are false.
• They mean the logic used to arrive at the
conclusion is faulty.
• Using informal fallacies in arguments weakens
our credibility and the credibility of our
“Remember, a fallacious argument may or may not have a
true conclusion. Either way, such an argument fails to
establish that conclusion properly.”
- J.P. Moreland
“We can meet [fallacies] in two ways: (1) when we use them
unwittingly and get caught by our audience and (2) when our
dialogue partners spring them on us as objections to our
argument. In both cases we need to keep our wits about us,
admit when we’ve been unfair and be gentle when we point
out the errors of others.”
- James Sire
Begging the Question
Abusive ad hominem
Appeal to hypocrisy
Appeal to the masses
Association to Hitler
Appeal to force
Poisoning the Well
Hypothesis Contrary to Fact
Fallacy of Association
Appeal to Tradition
Appeal to authority
Appeal to pity
Appeal to ignorance
Appeal to emotion
And many more…