Just as iron sharpens iron, so too hopefully these insights on Inductive reasoning versus
Deductive reasoning will help to sharpen your mind as we develop the meta-skill of thinking
about our thinking. Induction and Deduction are methods of reasoning
and when we look at their structure we approach them from the viewpoint of mental models,
where we essentially take a subject and objectify it so that we can manipulate it in our minds
more effectively and apply it across disciplines. As we hone our definitions of what inductive
and deductive reasoning are, we are developing razor-sharp thinking skills that lay at the
heart of Science and Philosophy. So, what is Induction and Deduction? Let us begin....
Ancient Greek dialecticians recognized the importance of how words are defined when applying
logic and this is still true today.
Induction, as we will handle it, is defined as:
"the inference of a general law from particular instances."
And Deduction is defined as: "The inference of particular instances by reference to a
general law or principle."
Deduction can sometimes be thought of as "top-down" thinking where the starting point is a universal
statement that is widely believed to be true and we then reason downward towards particular
inferences that follow logically from that universal statement we began with.
Induction is almost the mirror opposite as it can be thought of as "bottom-up" thinking
where we start with a sample of particular observations and infer a more universal statement
of truth that logically follows from the particular observations. Because Induction works in this
manner it is not guaranteed to produce absolutely true conclusions whereas Deduction if begun
with a True statement logically leads to true conclusions.
The shared purpose of Induction and Deduction is to use reason to prevent error.
The method of Induction infers a general rule from a few specific cases whereas the method
of Deduction shows that one theory follows from another.
(QUOTE:) "Inductive reasoning is based upon the axiom:
''What is true of the many is true of the whole." This axiom is based upon man's belief
in the uniformity of nature. Inductive reasoning is a mental ladder by which we climb from
particular facts to general laws, but the ladder rests upon the belief that the universe
is governed by law." -Your Mind and How to Use It - William W. Atkinson
Aristotle, who is responsible for much of the foundation of modern reasoning demonstrated
deduction with his syllogisms , which take a form such as:
"All men are mortal. Socrates is a man.
Therefore, Socrates is mortal. Aristotle's deductive syllogistic logic was
great for demonstrating logical truth.
Deduction tries to provide certainty and can guarantee that certainty if the argument is
sound which is to say that it is both logically correct or valid ***and*** is built with true
statements or premises.
Deductive reasoning can provide certainty if it is properly composed. When a deductive
argument is valid, its structure of premises or statements placed before the conclusion
and the conclusion are logically correct yet it is still possible to be logically correct
and have a false statement in the premises of the argument. When the premises are both
logically correct and actually true, then we arrive at certainty, which is called a
sound argument.
A Valid deduction can guarantee accuracy of the conclusion because deduction derives its
conclusion logically from its premises and Valid arguments are always logically consistent.
If the premises of the deduction are also known to be true then the conclusion is considered
Sound because it is both true and logically correct.
Aristotle's deductive syllogistic logic was great for bringing thoughts into harmony with
one another but when trying to discern the laws of nature as is so important in a scientific
age, a different method known as Inductive Logic was necessary.
Inductive reasoning can demonstrate that a conclusion is likely to be true but it can
not guarantee truth in the same logical manner that a sound deductive argument can.
Reasoning inductively is about developing conclusions that are probably true rather
than certainly true and is an important step in developing hypothesis and theories about
how the world works, which can then be tested more thoroughly as we gather greater data.
Inductive arguments can be considered either strong or weak similar to how a deductive
argument can be considered valid and or sound. A strong inductive argument provides a strong
reason for accepting the arguments conclusion whereas a weak inductive argument doesn't
offer a credible reason for accepting the conclusion.
John Stuart Mill is credited with formulating and articulating the logic of observation
and explanation we know as Inductive Logic, yet a much earlier figure, the Franciscan
friar Roger Bacon laid some of its groundwork.
Roger Bacon basically said that there are essentially two ways of knowing, by argument
and by experience. Having a question answered by an argument often will not make us feel
certain however, unless we can also draw upon results from experience.
All knowledge comes either through words or through experience. Argument vs. Experience.
Deductive logic and Inductive logic each aim to protect us against the potential errors
associated with these modes of conviction.
Induction can sometimes lead to superstitious beliefs because a person may observe an apparent
consistency and extrapolate a conclusion. If a visitor at a casino for example, just
started carrying a lucky rabbits foot and when they played their first slot machine,
they won a nice prize, they could conclude the lucky rabbits foot actually made them
luckier. If they win again with their lucky rabbits foot, it would most likely only strengthen
their belief. If however they subsequently had a run of poor luck, they would most likely
update their beliefs about whether or not the rabbits foot actually made them luckier,
a process or mental model in its own right called Bayesian thinking where a thinker modifies
the probability of the truth of a hypothesis as new evidence comes to light.
When we intermingle inductive inferences with deductive reasoning as we form and test hypothesis
we end up with what is considered The Scientific Method which is responsible for so many of
our present day technological achievements.
Induction is the process by which scientific inference allows us to jump from a particular
case to arrive at a universal principle.
Deduction is more knowledge based and induction is more observation based. When we begin with
a hypothesis for example, we use deduction to make predictions about what will occur.
True predictions uphold the theory whereas false predictions disprove it.
When using the Scientific Method it is the observations processed through inductive reasoning
which can lead to conclusions and these conclusions in turn may form new hypothesis which can
then be tested rigorously to see if they can be disproved.
Influential philosopher Karl Popper proposed that hypothesis cannot be proven, as we can
only ever show that certain predictions are false. Hence we have an almost hierarchical
intermingling of observations, ideas, and probable truth as we apply these two forms
of reasoning in our search for fact.
Legendary physicist Richard Feynman was quoted as saying, "Religion is a culture of faith;
science is a culture of doubt." Doubt is appeased by observing verifiable phenomenon through
our physical senses, utilizing processes such as the Scientific Method to observe, measure,
experiment, and test hypothesis often generated through inductive reasoning from the observations.
If a general law or truth is discovered in this manner, deductive reasoning can be used
to infer particular instances that can be predicted from this law.
Where religion differs from the Scientific Method is that whereas Science starts with
the observable, religion often starts at the other end with Spiritual-Mental general laws,
revelations, or truths that get applied deductively to determine the particulars of proper behavior.
Since much of religion deals with the mind or spirit, there is often little that can
be verified by our senses. This is essentially the territory of the battle that rages between
Science and Religion up to this day.
Hopefully what we've covered so far was helpful and has started to sharpen your thinking skills
and just to be sure lets review the main ideas we have covered in order to help solidify
this knowledge in our minds.
Inductive Reasoning is: "the inference of a general law from particular
instances."
And Deduction Reasoning is: "The inference of particular instances by
reference to a general law or principle."
Inductive Reasoning is often considered "bottom up" , whereas Deductive Reasoning is often
considered "Top down."
Both Inductive Reasoning and Deductive Reasoning are important aspects of the Scientific Method
where data is gathered "bottom up" through observations which can lead to Hypothesis
and the implications of these Hypothesis are tested in a more "top down" manner in order
to see if they can be falsified or whether they form the basis of a theory or general
principle which can then lead to even more predictions that can be tested or made use
of in this continuous cycle of knowledge discovery.
We can often notice these same processes in our own lives as we observe phenomena and
draw general conclusions or make predictions based on general principles. These processes
are constantly at play in the reasoning mind.
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