Part I: Understanding the Scientific Hypothesis
Part II: Writing the Scientific Hypothesis
 A hypothesis is an "educated guess." It
can be an educated guess about what
nature is going to do, or about why
nature does what it does.
What makes a statement a scientific hypothesis, rather
than just an interesting speculation?
A tentative, testable, and falsifiable explanation for
an observed phenomenon in nature.
A scientific hypothesis must meet 2 requirements:
 A scientific hypothesis must be testable, and;
 A scientific hypothesis must be falsifiable.
 Science proceeds by making observations of nature
and formulating educated guesses (hypotheses) about
how nature will behave for further investigation.
 If a hypothesis does not generate any observational
tests, there is nothing that a scientist can do with it.
 Arguing back-and-forth about what should happen, or
what ought to happen, is not the way science makes
progress. WHAT HAPPENS IS WHAT HAPPENS
REGARDLESS OF WHAT YOU THINK SHOULD
HAPPEN!
 Let’s see if … doing an experiment to see if a change
occurs is not a hypothesis, it is a fishing expedition.
 Testing to see if one “thing” is (better, faster, larger …
fill in the blank) than another “thing” is not a
hypothesis. Example: To see if soap A kills more
bacterial than soap B. That is consumer testing but is
not hypothesis-based science.
 A hypothesis is not a “hunch”, an unsupported idea, or
a random concept.
 A proper hypothesis is not formed as a question, it
should be a statement.
 This statement may or may not be true, but it is not a
scientific hypothesis. By its very nature it is not
testable.
 There are no observations that a scientist could make
to tell whether or not the hypothesis is correct.
 Ideas such as Hypothesis A are interesting to think
about, but science has nothing to say about them.
 Hypothesis A is a speculation, not a hypothesis.
 The word "predictions" can often cause confusion, since we
commonly think of a prediction as telling about something
that is going to happen in the future, like "Next year,
Lindsay Lohan will marry a frog."
 A scientific prediction is not something that is going
to happen, but rather something that is happening
right now, but no one has ever noticed.
 In other words, a prediction suggests a test for the
hypothesis. The test can be an experiment or it can be an
observation from nature.
 To say that a hypothesis "generates predictions"
means the same thing as saying the hypothesis "is
testable".
This hypothesis is testable, but it is not a scientific
hypothesis. Hypothesis B may be either correct or
wrong. If it is correct, there are several ways that its
correctness can be proven, including:
1.
2.
3.
A space probe sent from earth to explore the universe sends
back the news that it has discovered an inhabited planet. (This
news is later confirmed by other space probes.)
Radio telescopes on earth begin to receive signals from
somewhere in the Andromeda Galaxy that appear to be reruns
of the "I Love Telek" show.
Knock, Knock. "Greetings, earthling! I am Telek from the
planet Zoron in the Andromeda Galaxy. I have just landed in
your backyard. Take me to your leader.”
 So, if Hypothesis B is true, there are observations that




scientists could make that would prove its correctness.
But, the hypothesis may be wrong. (Most hypotheses are...)
If Hypothesis B is wrong, there is no test that will
prove it.
If one of our space probes never finds an inhabited planet,
it doesn't mean that one doesn't exist. If we never receive
signals from space, or Telek never lands in your back yard,
that does not prove that the hypothesis is wrong, either.
Hypothesis B is not falsifiable.
 Hypothesis C is a scientific hypothesis because:
 It is testable - pick 2 objects, and drop them. Of
course, you may have to provide a vacuum for them to
fall in, in order to remove air resistance from
consideration.
 It is falsifiable - If anyone finds 2 objects that don't
hit the ground at the same time and can show that it is
not due to air resistance, then she has proven the
hypothesis wrong. This hypothesis "sticks its neck out"
for every test. In theory and in practice, if Hypothesis
C were wrong, it would be very easy and
straightforward to show it.
 It is relatively easy to gather evidence for just about any
idea, but a hypothesis is essentially worthless unless it
is "risky" - it must make predictions that could
contradict it.
 The process of gaining real confidence in a hypothesis,
then, is not in accumulating evidence in its favor, but
rather in showing that situations that could establish
its falsity don't, in fact, happen.
 Note that it is very easy to prove Hypothesis C wrong (if it
were), but it is impossible to prove it correct!
 Since Hypothesis C states that any pair of objects behaves
in a certain way, in order to prove it correct, all possible
combinations of objects that exist (or have ever, or will ever
exist) must be tested. This is clearly not possible.
 As we test Hypothesis C more and more, we can get more
and more confident in its truth, but we can never be
absolutely sure.
 Someone could always come up with 2 objects tomorrow
which don't behave exactly as Hypothesis C says they
should, and this would make Hypothesis C incorrect.
 It sometimes bothers people that scientific facts,
hypotheses, laws, and theories generally can't be
proven to be true.
 It generally doesn't bother scientists, however. You
might say, "Can't scientific hypotheses be phrased so
that they could be proven true?"
 Hypothesis D is a scientific hypothesis - it is testable, and it is




falsifiable. There are two problems with it, however:
It is a very wimpy hypothesis. Compared to Hypothesis C, which
is quite powerful and useful, Hypothesis D is practically useless,
and;
Hypothesis D can't be proven correct, either!
Who is to say that someone won't show up tomorrow with some
brand new, super-sophisticated, high-tech measuring
instrument and say "Look! My measuring device clearly shows
that the little object hits the ground fully a half a trillionth of a
second before the big one."
The best we can ever say (as scientists) is something like, "It
certainly appears to me at this time that both objects hit the
ground at the same time." Even timid little Hypothesis D cannot
be proven to be absolutely true!
 If a hypothesis fails a test, it cannot be true, and it must be
modified or discarded.
 In science, if there is a conflict between observation and
hypothesis, the hypothesis loses. It doesn't matter whose
hypothesis it is or how famous they are - if the hypothesis does
not conform to reality it must be rejected.
 Personal anecdote: A scientist I know very well spent 10 years
gathering evidence for a hypothesis and never falsified it, that is
until this year. His hypothesis failed scrutiny based on ONE
REPEATABLE EXPERIMENT even though 10 years of extensive
research said it was likely correct. He discarded the hypothesis.
He is actually happy with this. Why? Because “Not only do I now
know more about nature, but I also will not be spending another
10 years chasing after something that is just plain wrong.”
With a QUIZ!!!
 True
 False
 True
 False
 True
 False
 True
 False
A. Testable
B. Falsifiable
C. Wrong
D. Correct
E. Both A and B
A. Testable
B. Falsifiable
C. Wrong
D. Correct
E. Both A and B
 Found in a science book
 Nonsense! Hypotheses never become theories!
 Agreed upon by several competent people
 Tested multiple times by multiple methods and
scientists, and never once be reliably falsified
 Found in a science book
 Nonsense! Hypotheses never become theories!
 Agreed upon by several competent people
 Tested multiple times by multiple methods and
scientists, and never once be reliably falsified
The scientists should report that it turns blue.
B. The experiment must be ignored.
C. The experiment must be repeated until someone gets the
correct results.
D. The hypothesis is wrong, it must be discarded or modified.
E. The experiment must be modified to produce the correct
results.
A.
The scientists should report that it turns blue.
B. The experiment must be ignored.
C. The experiment must be repeated until someone gets the
correct results.
D. The hypothesis is wrong, it must be discarded or modified.
E. The experiment must be modified to produce the correct
results.
A.
 Scientific because it is testable
 Scientific because it deals with scientific things
 Not scientific because it is not testable
 Not scientific because it is not falsifiable
 None of these
 Scientific because it is testable
 Scientific because it deals with scientific things
 Not scientific because it is not testable
 Not scientific because it is not falsifiable
 None of these
 Data
 Theory
 Law
 Hypothesis
 Conclusion
 Data
 Theory
 Law
 Hypothesis
 Conclusion
If [Hypothesis] is correct, and I
do [Experimental Methods],
Then [Prediction] will happen.
(IF hypothesis, AND method,
THEN prediction)
 Problem: Battery operated car does not go fast enough.
 Engineering goal: Make the car go faster
 Hypothesis: Electricity is more powerful than batteries
 Prediction (with methods): Powering the car with
electricity will make the car go faster.
 Scientific hypothesis [Putting it all together]:
If [Hypothesis] is correct, and I do [Experimental
Methods], Then [Prediction] will happen.
 Problem: Battery operated car does not go fast enough.
 Engineering goal: Make the car go faster
 Hypothesis: Electricity is more powerful than batteries
 Prediction (with methods): Powering the car with
electricity will make the car go faster.
 Scientific hypothesis [Put it all together]:
If electricity is more powerful than batteries,
and I replace batteries with electricity from the
outlet, then my car will go faster.
Observation: flashlight doesn’t work.
1. Explanation (hypothesis): the batteries are dead.
2. Explanation (hypothesis): the bulb is burned out.
Prediction (with methods): replacing the batteries will
make the flashlight work.
Scientific Hypothesis:
If [Hypothesis] is correct, and I do [Experimental
Methods], Then [Prediction] will happen.
Observation: flashlight doesn’t work.
1. Explanation (hypothesis): the batteries are dead.
2. Explanation (hypothesis): the bulb is burned out.
Prediction (with methods): replacing the batteries will
make the flashlight work.
Scientific Hypothesis:
If the dead battery hypothesis is correct, and I
replace the batteries with new ones, then the
flashlight should work.
Observation: flashlight doesn’t work.
1. Explanation (hypothesis): the batteries are dead.
2. Explanation (hypothesis): the bulb is burned out.
Prediction (with methods): replacing the batteries will
make the flashlight work.
Scientific Hypothesis: If the dead battery hypothesis is
correct, and I replace the batteries with new ones, then
the flashlight should work.
 Flashlight works! Test of hypothesis #1 supports/does
not falsify the hypothesis.
 The above hypothesis is both testable and falsifiable.
 Observation: When our hands are cold, we lose our fine
motor skills. So breaking toothpicks requires fine motor
skills, doesn’t it? Let’s do an experiment with toothpicks
where we break them with our hands at two different
temperatures and see what happens.
 Hypothesis: I can break more toothpicks with my hand
when it is warm than I can when my hand is cold.
 No. This is simply a prediction, not a hypothesis in the
scientific sense.
 This phrasing shifts away from investigating cause and
toward simply confirming an observation.
 Observation: When our hands are cold, we lose our fine
motor skills. So breaking toothpicks requires fine motor
skills, doesn’t it? Let’s do an experiment with toothpicks
where we break them with our hands at two different
temperatures and see what happens.
 Hypothesis: If I break toothpicks for one minute with my
warm hand and then with my cold hand, then I will break
more toothpicks with my hand when it is warm.
 No. This is a method followed by a prediction—there is still
no apparent reason for doing this experiment. What
explanation is being tested?
 Observation: When our hands are cold, we lose our fine
motor skills. So breaking toothpicks requires fine motor
skills, doesn’t it? Let’s do an experiment with toothpicks
where we break them with our hands at two different
temperatures and see what happens.
 Hypothesis: If I break toothpicks for one minute with my
warm hand and then for one minute with my hand after
soaking it in ice water for five minutes, then I will break
more toothpicks with my hand when it is warm BECAUSE
low temperatures suppress muscle contractions and thus
fine motor skills.
 Almost. But this form puts the hypothesis being tested,
that cold suppresses muscle contractions, at the end of the
statement, in the conclusion, rather than in the beginning
where the hypothesis belongs. Also, the use of the word
Because suggests truth and removes the necessarily
tentative nature of the hypothesis.
 Observation: When our hands are cold, we lose our fine
motor skills. So breaking toothpicks requires fine motor
skills, doesn’t it? Let’s do an experiment with toothpicks
where we break them with our hands at two different
temperatures and see what happens.
 Hypothesis: If low temperatures suppress muscle
contractions and thus fine motor skills, and I break
toothpicks for one minute with my warm hand and then
for one minute with my hand after soaking it in ice water
for five minutes, then I will break more toothpicks with my
hand when it is warm.
 Yes. This begins with the hypothesis that low temperatures
suppress muscle contractions, and beginning with the
word if makes the hypothesis tentative. This form also
includes how this hypothesis will be tested, and ends with
a specific, measurable, predicted outcome of the
experiment.
 Silver salmon (Oncorhynchus kisutch) are born in the
headwaters of Pacific Northwest streams. Young salmon
grow and mature sexually in the Pacific Ocean. By tagging
young salmon, biologists discovered that mature salmon
actually return to reproduce in precisely the same
headwaters where they were born some years earlier.
 This discovery raised a very interesting causal question:
How do returning salmon find their home stream?
 By borrowing explanations from other animal taxa, A. D.
Hasler (1960) generated three hypotheses for salmon
navigation: (1) salmon use sight; (2) salmon smell
chemicals specific to their home stream; and (3) salmon
use the Earth’s magnetic field.
Hasler, Arthur D. 1960. Guideposts of Migrating Fishes. Science 132:785-792
 If … salmon find their home stream by sight (sight
hypothesis), and … a group of non-blindfolded salmon
and a group of blindfolded salmon from the Issaquah
and East Fork streams are released below the fork
where the two streams join (planned test), then … the
non-blindfolded salmon should be recaptured in their
home stream more frequently than the blindfolded
salmon (prediction).
Lawson, Antone E. 2004. The Nature And Development of Scientific Reasoning: a Synthetic View. International Journal of
Science and Mathematics Education 2:307–338.
Now it is time for you to be the judge!
“If a plant receives fertilizer, then they will grow to be
bigger than a plant that doesn’t receive fertilizer.”
Prediction only
Prediction (with methods)
Hypothesis only
Hypothesis and Prediction
Research Hypothesis (Hypothesis, Methods, Prediction)
Now it is time for you to be the judge!
“If a plant receives fertilizer, then they will grow to be
bigger than a plant that doesn’t receive fertilizer.”
Prediction only
Prediction (with methods)
Hypothesis only
Hypothesis and Prediction
Research Hypothesis (Hypothesis, Methods, Prediction)
Now it is time for you to be the judge!
“The hypothesis of this study was that cattle presence
would have an adverse impact on the terrestrial
salamander population.”
Prediction only
Prediction (with methods)
Hypothesis only
Hypothesis and Prediction
Research Hypothesis (Hypothesis, Methods, Prediction)
Now it is time for you to be the judge!
“The hypothesis of this study was that cattle presence
would have an adverse impact on the terrestrial
salamander population.”
Prediction only
Prediction (with methods)
Hypothesis only
Hypothesis and Prediction
Research Hypothesis (Hypothesis, Methods, Prediction)
Now it is time for you to be the judge!
“It is hypothesized that in the early time intervals of data
collection, the cells fed with TGF Beta will at first be
suppressed by the hormone.”
Prediction only
Prediction (with methods)
Hypothesis only
Hypothesis and Prediction
Research Hypothesis (Hypothesis, Methods, Prediction)
Now it is time for you to be the judge!
“It is hypothesized that in the early time intervals of data
collection, the cells fed with TGF Beta will at first be
suppressed by the hormone.”
Prediction only
Prediction (with methods)
Hypothesis only
Hypothesis and Prediction
Research Hypothesis (Hypothesis, Methods, Prediction)
Now it is time for you to be the judge!
“Ground level ozone will be higher in areas of Fairfield,
Iowa, with more traffic.”
Prediction only
Prediction (with methods)
Hypothesis only
Hypothesis and Prediction
Research Hypothesis (Hypothesis, Methods, Prediction)
Now it is time for you to be the judge!
“Ground level ozone will be higher in areas of Fairfield,
Iowa, with more traffic.”
Prediction only
Prediction (with methods)
Hypothesis only
Hypothesis and Prediction
Research Hypothesis (Hypothesis, Methods, Prediction)
Now it is time for you to be the judge!
“Earthworm activity will alter the chemical trajectory of
leaf litter from background fungal dominated decay
paths.”
Prediction only
Prediction (with methods)
Hypothesis only
Hypothesis and Prediction
Research Hypothesis (Hypothesis, Methods, Prediction)
Now it is time for you to be the judge!
“Earthworm activity will alter the chemical trajectory of
leaf litter from background fungal dominated decay
paths.”
Prediction only
Prediction (with methods)
Hypothesis only
Hypothesis and Prediction
Research Hypothesis (Hypothesis, Methods, Prediction)
Now it is time for you to be the judge!
“If pH is a factor in the decomposition of H2O2, then
lowering the pH will inhibit the rate.”
Prediction only
Prediction (with methods)
Hypothesis only
Hypothesis and Prediction
Research Hypothesis (Hypothesis, Methods, Prediction)
Now it is time for you to be the judge!
“If pH is a factor in the decomposition of H2O2, then
lowering the pH will inhibit the rate.”
Prediction only
Prediction (with methods)
Hypothesis only
Hypothesis and Prediction
Research Hypothesis (Hypothesis, Methods, Prediction)
Now it is time for you to be the judge!
“It is hypothesized that if the bridge’s structural width is
changed from 40 mm to 30 mm to 20 mm, then the
structural efficiency will increase respectively.”
Prediction only
Prediction (with methods)
Hypothesis only
Hypothesis and Prediction
Research Hypothesis (Hypothesis, Methods, Prediction)
Now it is time for you to be the judge!
“It is hypothesized that if the bridge’s structural width is
changed from 40 mm to 30 mm to 20 mm, then the
structural efficiency will increase respectively.”
Prediction only
Prediction (with methods)
Hypothesis only
Hypothesis and Prediction
Research Hypothesis (Hypothesis, Methods, Prediction)
Now it is time for you to be the judge!
“Dye affects the efficiency of a solar cell by being able to
absorb more light into the solar cell as opposed to no
dye. Thus, the cell with no dye should not be able to
conduct electricity.”
Prediction only
Prediction (with methods)
Hypothesis only
Hypothesis and Prediction
Research Hypothesis (Hypothesis, Methods, Prediction)
Now it is time for you to be the judge!
“Dye affects the efficiency of a solar cell by being able to
absorb more light into the solar cell as opposed to no
dye. Thus, the cell with no dye should not be able to
conduct electricity.”
Prediction only
Prediction (with methods)
Hypothesis only
Hypothesis and Prediction
Research Hypothesis (Hypothesis, Methods, Prediction)
Now it is time for you to be the judge!
“Because a prescribed burn is lower in intensity than a
wildfire, prescribed burns can significantly reduce
mercury emissions from a subsequent fire.”
Prediction only
Prediction (with methods)
Hypothesis only
Hypothesis and Prediction
Research Hypothesis (Hypothesis, Methods, Prediction)
Now it is time for you to be the judge!
“Because a prescribed burn is lower in intensity than a
wildfire, prescribed burns can significantly reduce
mercury emissions from a subsequent fire.”
Prediction only
Prediction (with methods)
Hypothesis only
Hypothesis and Prediction
Research Hypothesis (Hypothesis, Methods, Prediction)
Now it is time for you to be the judge!
“It is hypothesized that the structural and functional
integrity of the system as a whole is dependent on nerve
activity.”
Prediction only
Prediction (with methods)
Hypothesis only
Hypothesis and Prediction
Research Hypothesis (Hypothesis, Methods, Prediction)
Now it is time for you to be the judge!
“It is hypothesized that the structural and functional
integrity of the system as a whole is dependent on nerve
activity.”
Prediction only
Prediction (with methods)
Hypothesis only
Hypothesis and Prediction
Research Hypothesis (Hypothesis, Methods, Prediction)
Now it is time for you to be the judge!
“If parthenolide is a substrate specific inhibitor in signal
transduction, and I examine the effects of parthenolide on
the secretion of 5-HT through two independent pathways
using a platelet-based model, then parthenolide should
inhibit the secretion of 5-HT only through the PKC pathway.”
Prediction only
Prediction (with methods)
Hypothesis only
Hypothesis and Prediction
Research Hypothesis (Hypothesis, Methods, Prediction)
Now it is time for you to be the judge!
“If parthenolide is a substrate specific inhibitor in signal
transduction, and I examine the effects of parthenolide on
the secretion of 5-HT through two independent pathways
using a platelet-based model, then parthenolide should
inhibit the secretion of 5-HT only through the PKC pathway.”
Prediction only
Prediction (with methods)
Hypothesis only
Hypothesis and Prediction
Research Hypothesis (Hypothesis, Methods, Prediction)
A farmer observes that one edge of his onion field
produces taller plants and larger onions. This same edge
borders a prairie that the farmer has been slowly
restoring over the last 10 years. Every two years the
farmer initiates a controlled burn in the prairie to clear
out invasive species. Each year he burns the prairie, it
grows back greener than in the years he doesn’t burn it.
 Are brightly colored leaves in the fall a warning to
potential herbivores?
 Why do some bird species arrive at their breeding
grounds at the same time every spring, regardless of
spring conditions?