What is a thesis defense?

A thesis defense has two parts: a thesis and a defense.  The second mistake
many students make is not knowing what their thesis is.  The third mistake
is not knowing how to defend it.  (The first mistake
is described later.)

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What is a thesis?

Your thesis is not your dissertation.  Neither is it a one-liner about what
you are doing.}  Your thesis is ``a position or proposition that a person
(as a candidate for scholastic honors) advances and offers to maintain by
argument.'' [Webster's 7th New Collegiate Dictionary]  ``I looked at how
people play chess'' is not a thesis; ``people adapt memories of old games
to play new games'' is.  A thesis has to claim something.

There are many kinds of theses, especially in engineering, but most of them
can be lumped into one of the following classes:

   1    process X is a feasible way to do task Y

   2    process X is a better way to do task Y than any previously
        known method

   3    task Y requires process X

   4    people use process X to do task Y

   5    process X is a terrible way to do Y, or 
    
   6    people don't use process X


Feel free to substitute ``process X'' with ``memory organization X'' or
whatever else might make one theory different from another.

Besides being a proposition, a thesis has to have another property: it must
say something new. 
``Understanding target images requires context'' is not a thesis (except
maybe in a linguistics department);  ``process X is a feasible mechanism
for adding context sensitivity to target image understanding'' is, as
is ``context is not required for visual understanding.''

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What is a defense?

A defense presents evidence for a thesis.  What kind of evidence is
appropriate depends on what kind of thesis is being defended.

Thesis: process X is a feasible way to do task Y

    One defense for this kind of claim is an analysis of the complexity, or
completeness, or whatever, 
of the theoretical algorithm.  In engineering, the more common defense is
based on empirical results
from running an experiment.A good defense here means more than one example,
and answers to questions such as the following.  What are the capabilities
and limits of your experiment?  How often do
the things that your experiment does come up in the real world?  What's
involved in extending it?  If it's easy to extend, why haven't you?  

If your example a piece of a larger system, how realistic are your
assumptions about input and output?


Thesis: process X is a better way to do task Y than any previously known
method

    The same kind of defense applies here as in the previous case, but now
serious comparisons with previous systems is required.  Can your result do
the same examples the previous results did, or can you make them do yours?
Can you prove they couldn't do your examples? If you claim to be more
efficient, what are you measuring?


Thesis: task Y requires process X

    This is usually defended by a logical argument.  It is usually very
tough to do, even if the argument doesn't have to be formalized.


Thesis: people use process X to do task Y

Many students make the mistake of picking this kind of thesis to defending.
 It requires serious experimental evidence to defend, unless your real
thesis is of the previous form, i.e., only process X is possible.  Selected
excerpts from protocols and surveys of your "officemates" are not
scientific evidence,
no matter how much they might have inspired your work.


Thesis: process X is a terrible way to do Y, or people don't use process X

    This is a reasonable thesis if process X is a serious contender.  The
defense would be an analysis of the limits of process X, i.e., things it
can't do, or things it does wrong, along with evidence that those things
matter.


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I have lots of theses in my dissertation.  Which one should I pick for my
defense?

Defending a real thesis is hard.  If you think you have a lot of theses,
you probably just have a bunch of undefended claims.  One good thesis, or
two so-so theses, with adequate description and defense, is more than
enough to fill up a dissertation.


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I have the opposite problem. I don't think I have any thesis by these
standards.

Highly unlikely.  If you're bright, educated, and have worked hard on a
topic for more than a year, you must have learned something no one else
knew before.  {\em The first mistake that students make is to think that a
thesis has to be grander than the theory of relativity.}  A thesis should
be new and interesting, but it doesn't have to change the foundations of
all we believe and hold dear.  

Don't try to come up with a thesis first, and then investigate it.  Start
by exploring some task domain.
Take some initial ideas and push them hard for a year or so.  Now, stop and
think about what you've
done and what you've learned.  Among your accomplishments and experience,
there will be several good candidate theses.  Pick one.  Test it out on
your advisor and other faculty members.  Test it out on other students.  Is
it a claim that you can describe clearly and briefly?  Is it a claim that
anyone cares about?
Is it a claim that people don't find perfectly obvious, or if they do find
it obvious, can you can convince them that it could easily be false?

Once you refined your claim into a good thesis, now you can determine what
kind of defense is appropriate for it and what more you need to do.  This
is where the hard part comes, psychologically, 
because to create a defense for your thesis, you're going to have to attack
it harder than anyone else.  What happens if the thesis fails?  Negate it
and defend that!  In a year or so of focussed research, you should be ready
for a real thesis defense.

See how easy it is, once you know how?

(C) 1995, Can be freely distributed.
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