Professor Norman Swartz|
Simon Fraser University
The Presuppositions of Empirical Research
A carpet vendor has to measure her customer's living room for
some new broadloom. She has forgotten her tape measure, but does
have a meterstick. She lays the meterstick on the floor, snug up
against the wall, with the left edge of the stick in one corner
of the room. She then makes a pencil mark at the right edge.
Next she shifts the stick right until the left edge of the stick
is at her mark, and again marks the right edge. She does this
three times, but then finds that less than a full length remains
to be measured. She turns the stick around so that the zero is
now at the right side and lays it in the right corner and notes
that her last pencil mark is at 70 cm. She concludes that the
wall she is measuring is 3.7 meters in length. She then measures
the opposite wall and concludes that it, too, is 3.7 meters in
length. She then repeats the process for the remaining two
opposite walls, and finds that they each measure 4.1 meters. To
see if the room is rectangular, she runs a piece of twine from
one corner to its opposite, pulls the twine taut and then cuts it
to fit exactly. She then uses the same piece of twine on the
other two corners to see if they are the same distance apart as
the first two. The twine fits exactly. On the basis of these
measurements, she concludes that the area of the room is
Think about this: What are some of the presuppositions in the
foregoing scenario which would have to be true in order that the
carpet vendor's conclusion be true? Here is a (partial) list:
- The meterstick does not change length as it is moved about in
- The meterstick she is using is in fact well made, and is (very
nearly) 1 meter in length. (Remember, wooden metersticks – the
cheap ones which you are likely to find in lumberyard sales –
often shrink with age.)
- Pencil marks do not move about on walls.
- A string pulled taut twice will be the same length on both
- The area of a four-sided room, whose opposite sides are equal and
whose diagonals are equal, may be determined by multiplying its
width by its length.
- Lengths add like numbers.
- The order in which the measurements are taken is irrelevant, i.e.
would be the same if they had been taken in the reverse
- The walls are not bowed.
- Etc., etc., etc.
It was common knowledge in
Jenner's time that a person could
catch smallpox only once. Many people tried to inoculate
themselves with matter from smallpox sores. They hoped to catch
a light case of the disease, and then be immune to it for the
rest of their lives. Lady Mary Wortley Montagu, an English
author, had introduced this method in England in 1718. But the
method was dangerous.
Here is a (partial) list of presuppositions that would have to be true
for Jenner's conclusion to be true:
Jenner began experimenting in his
home town, Berkeley,
Gloucestershire. Many people there believed that diarymaids who
had caught cowpox could not catch smallpox. Cowpox is a minor
disease that causes a few sores on the hands but carries little
danger of disfigurement or death. In 1796, Jenner took matter
from the hand of Sarah Nelmes, a local dairymaid. She had become
infected with cowpox while milking the cows. Jenner then made
two cuts on the arm of James Phipps, a healthy eight-year old
boy, and inserted the matter from one of Sarah's cowpox sores.
The boy then caught cowpox. Six weeks later, Jenner introduced
smallpox matter into the boy's arm. Ordinarily fatal, the
smallpox matter had no effect. (World Book Encyclopedia,
1979, "Edward Jenner", vol. 11, p. 73)
Here are a few presuppositions which have to be made in some
other medical experiments, but not(!!!) in Jenner's (in 1796).
- Nelmes and others who appeared to have cowpox, really did,
i.e. did not have some other disease having symptoms similar to
cowpox. (If Nelmes and others in Berkeley had had some other
disease, then other doctors, in other towns, using the matter
from other persons who did in fact have cowpox, might not have
succeeded in protecting their patients from smallpox.)
- Phipps and other subjects whom Jenner inoculated had not had
mild, undetected, cases of smallpox earlier.
- There was nothing in the water or atmosphere in Berkeley that
conferred immunity against smallpox on everyone living in that
- Jenner's instruments were sterile or, at the very least, not
the source of some unknown material that conferred immunity
- The material, in being transferred from the donor to the
recipient, was not subjected to anything in the process of
transferral that would have created the immunity-conferring
- Jenner himself did not have (mystical? magical?) curative
powers (perhaps even unknown to himself). (There was nothing on
his skin, or in his exhalations, that could confer immunity
- There are not different strains of cowpox such that one
strain (such as might be found in Berkeley) would confer immunity
against smallpox, but that other strains (in other locales) might
- There was nothing else in the history of the subjects whom
Jenner inoculated that was responsible for their immunity to
smallpox (e.g. they did not all attend the same school or church,
did not all work in the same factory, etc.).
- The subjects who were inoculated with cowpox were genuinely
immune to smallpox: they were not asymptomatically incubating the
disease, only to come down with a fatal case some time later
(e.g. several years).
- The immunity to smallpox was relatively long lasting.
Persons who were (or seemed to be) immune to smallpox six weeks
after having being inoculated with material from cowpox sores
would also be immune to smallpox for a longer period. (What we
now call "booster inoculations" would not be needed frequently,
or even worse, at shorter and shorter intervals.)
- The time of day – of the taking of the material from a cowpox
lesion, of the transferring that matter to another person, and of
the subsequent inoculating the latter person with smallpox
material – was irrelevant to the outcome (i.e. the time of day
was not a causal factor). Ditto for temperature, atmospheric
pressure, season, and weather conditions.
- Persons' diets did not affect the outcome of the experiment.
- Persons' age did not affect the outcome of the experiment.
- Persons' race did not affect the outcome of the experiment.
- If a donor were pregnant, that would not affect the outcome
of the experiment; more exactly, pregnancy is not a causal
factor, either positively or negatively. (Note: one would want
to be very cautious [and have done some experimenting on animals]
before inoculating pregnant women with either cowpox or smallpox
material – it might have a deleterious affect on the fetus.)
- The particular time of a woman's menstrual cycle, whether she
was the donor or the recipient of the cowpox material, did not
affect the outcome of the experiment.
- Persons' prior medical history – e.g. whether they had had
pneumonia, dysentery, gout, whooping cough, etc. – would not
affect the outcome of the experiment.
- Transferring matter from a smallpox sore to a cut in the skin
of another person would induce smallpox in that second person
(provided that the second person had not previously had either
cowpox or smallpox). (Note: this particular presupposition was,
presumably, already fairly well established by Montague.)
- It did not matter from where on one's body – whether from the
arm, the leg, the neck, etc. – the cowpox and smallpox matter was
taken; nor did it matter where, on the body of another person,
this material was inserted.
- Smallpox immunity was not being conferred by something
attendant upon the inoculation, e.g. by parallel incisions in
- The immunity was not being conferred by a chemical reaction
between the skin (or blood) of the person being inoculated and
the particular metal (iron?) of Jenner's knife (scalpel).
- There was nothing done to, or by, the persons (who had been
inoculated with smallpox matter) after their inoculations that
would prevent their contracting smallpox, i.e. whatever immunity
to smallpox they exhibited was the result of what had happened to
them before their inoculation with smallpox matter.
- Immunity to smallpox cannot be induced/conferred by the
subject's belief that he/she has been given an effective
immunization. (In vocabulary which has become current since the
late 1940s, we would say that the immunity is not a 'placebo
- The lifestyles of the donors and recipients, e.g. whether
they were physically active or whether they were fairly
sedentary, would not affect the outcome of the experiment.
- It was not the treatment for cowpox (e.g. applying salves)
that conferred the immunity to smallpox.
- The mere transferring of matter (flesh and/or bodily fluids)
from the body of a person infected with cowpox to the body of
another person does not confer on that latter person immunity to
smallpox; the transferred matter must be from festering sores.
- The agents of smallpox and cowpox are germs (bacteria, viruses, etc.). (The germ theory of disease was not to become generally accepted for another two to four decades.)
- Human beings have an immune system which attacks foreign organisms in the body and which, in some instances, produces lifelong antibodies.
- The immune system can attack foreign organisms anywhere in the body.
- The agents of infection are carried throughout the body by the blood stream.