| The description of induction and
deduction in the Manual on pp.13-19 is effective. Here are a few
more examples to make it still more effective. All were gleaned
from the Internet.
The first comes from the Catholic Encyclopaedia.
"Induction is opposed to deduction only in the sense that
it approaches reality from the side of the concrete and
individual, while deduction does so from that of the abstract and
the universal." This is clearly a very general statement and
is not particularly appropriate for our discussion of the
scientific method.
The second is redrawn from William M. K. Trochim’s The
Research Methods Knowledge Base, http://trochim.human.cornell.edu/kb/dedind.htm
"In logic, we often refer to the broad methods of
reasoning as the deductive
and inductive
approaches.
| Deductive
reasoning works from the more general to the more specific.
Sometimes this is informally called a "top-down"
approach. We might begin with thinking up HYPOTHESIS a theory
about our topic of interest. We then narrow that down into
more specific hypotheses
that we can test. We narrow down even further when we
collect observations to address the hypotheses. This
ultimately leads us to be able to test the hypotheses with
specific data– a confirmation (or not) of our original
theories.
|
 Inductive
reasoning works the other way, moving from specific
observations to broader generalizations and theories.
Informally, we sometimes call this a "bottom- up"
approach (please note that it’s "bottom up" and
not "bottoms up" which is the kind of thing the
bartender says to customers when he’s trying to close for
the night!). In inductive reasoning, we begin with specific
observations and measures, begin to detect patterns and
regularities, formulate some tentative hypotheses we can
explore, and finally end up developing some general
conclusions or theories. |
These two methods of reasoning have a very
different "feel" to them when you’re conducting
research. Inductive reasoning, by its very nature, is more
open-ended and exploratory, especially at the beginning.
Deductive reasoning is more narrow in nature and is concerned
with testing or confirming hypotheses. Even though a particular
study may look like it’s purely deductive (e.g., an experiment
designed to test the hypothesized effects of some treatment on the
outcome), most social research involves both inductive and
deductive reasoning processes at some time in the project. In
fact, it doesn’t take a rocket scientist to see that we could
assemble the two graphs above into a single circular one that
continually cycles from theories down to observations and back up
again to theories. [This shows much better in the original]. Even
in the most constrained experiment, the researchers may observe
patterns in the data that lead them to develop new theories".
(William K. Trochim, 2002)
Only part of a third example is reproduced here [Deduction and
Induction, http://falcon.jmu.edu/
~omearawm/deduction.html].
It is well worth reading, with excellent examples of both
inductive and deductive which clearly make the distinction between
the two modes of reasoning. It also has a good description of the
scientific method.
The fourth example is an Introduction to the Scientific Method
which appears to have been an appendix to a Physics Laboratory
Manual. It can be found at http://teacher.nsrl.rochester.edu/phys_labs/AppendixE/AppendixE.html
The fourth example tabulates the differences between the two
methods as shown below. http://www.owlnet.rice.edu/~chem121/class/chemproj/addresources.dedind.htm
|
Deduction |
Induction |
|
1. In a valid deductive argument, all of the
content of the conclusion is present, at least implicitly,
in the premises. Deduction is nonampliative. |
1. Induction is ampliative. The
conclusion of an inductive argument has content that goes
beyond the content of its premises. |
|
2. If the premises are true, the conclusion
must be true. Valid deduction is necessarily truth
preserving. |
2. A correct inductive argument may have
true premises and a false conclusion. Induction is not
necessarily truth preserving. |
|
3. If new premises are added to a valid
deductive argument (and none of its premises are changed or
deleted) the argument remains valid. Deduction is erosion-proof. |
3. New premises may completely undermine a
strong inductive proof. Induction is not erosion proof. |
|
4. Deductive validity is an all-or-nothing
matter; validity does not come in degrees. An argument is
totally valid, or it is invalid. |
4. Inductive arguments come in different degrees
of strength. In some inductions the premises support the
conclusions more strongly than others. |
|
