What’s the difference between deductive and inductive reasoning?
Science is about discovering the reasons why things happen in the
universe, so it shouldn’t be a surprise to learn that scientific knowledge is
gained through reasoning. There’s more than a single way to reason, though,
and one plays a much bigger role in science than any other.
Deduction is a form of reasoning that uses broad, generalized facts to
draw conclusions about specific questions or events. For example, let’s say
you go to bed one night, wake up at dawn, and the ground is covered in a
layer of fresh snow. You also see a line of tiny footprints imprinted on the
snow. Using deductive reasoning, you know an animal walked there during
the night. You reach this conclusion because, a: animals leave footprints
when they walk through snow; and b: the snow fell during the night;
therefore, c: an animal walked across the snow during the night. If a and b
are true, then c must be true.
Deduction doesn’t really lead to new knowledge, though. When a more
general truth is already known, deduction simply proves that more specific
instances are true as well. You know that gravity causes objects to fall when
they’re dropped, and an apple is an object, so concluding that an apple will
fall when it’s dropped isn’t particularly informative.
Science is mainly based on induction, which, in a way, is the opposite of
deduction. Inductive reasoning uses specific examples to draw more general
conclusions. Going back to the tracks in the snow, induction might lead you
to conclude that a possum walked across the yard at night. In five years,
you’ve never observed any animals but possums during the night. The tracks
also appear to have been made by a small, four-legged animal. Therefore, it
was most likely a possum that crossed the yard. Inductive reasoning leads to
most likely conclusions, but there’s always a chance, no matter how small,
that something else is the answer.
Scientific knowledge is gained through inductive reasoning. Scientists
observe specific events, whether they occur in nature or in controlled
experiments. Then, based on the accumulated evidence from many specific
observations, they draw conclusions about the world. Much of what we think
of as scientific fact began as a hypothesis. A hypothesis is an explanation—
based on background knowledge and
observations—for very specific events that occur in
the natural world. Hypotheses are tested in scientific
experiments, and if not proven wrong, they often
become the building blocks of theories. A theory is
an explanation that applies to multiple events. In
other words, a theory is a broader, more general
explanation. Since science is based on induction,
even the strongest hypotheses and theories have to
be adjusted if new evidence appears.
reasoning: the process of forming conclusions, judgments, or inferences based on facts or other evidence
deduction: reasoning from the general to the specific, in which a conclusion must be true because it’s based on true statements
induction: reasoning
that uses specific
events or facts to draw
more general
conclusions
evidence: something that helps either prove or disprove a conclusion
theory: a statement that explains a group of facts or phenomena; most accepted theories have been repeatedly tested and can be used to make predictions about nature
hypothesis: a statement that explains a specific fact or phenomenon; a hypothesis is tested in each scientific experiment
The example of
deductive reasoning
that’s probably more
famous than any other
is: Socrates is a man.
All men are mortal.
Therefore, Socrates is
mortal.
