Hypothetical-deductive method is a very important method for testing theories or hypotheses and is one of the most basic methods common to all scientific disciplines.
1. Basic definition of hypothetical-deductive reasoning
Hypothetical-deductive method (HD method) is a very important method for testing theories or hypotheses. The HD method is one of the most basic methods common to all scientific disciplines including biology, physics, and chemistry. Its application can be divided into five stages:
1. Form many hypotheses and evaluate each hypothesis
2. Select a hypothesis to be tested
3. Generate predications from the hypothesis
4. Use experiments to check whether predictions are correct
5. If the predictions are correct, then the hypothesis is confirmed. If not, the hypothesis is disconfirmed.
HD reasoning involves starting with a general theory of all possible factors that might affect an outcome and forming ahypothesis; then deductions are made from that hypothesis to predict what might happen in an experiment.
In scientific inquiry, HD reasoning is very important because, in order to solve science problems, you need to make hypotheses. Many hypotheses can't be tested directly; you have to deduce from a hypothesis and make predictions which can be tested through experiments.
2. Review of hypothetical-deductive reasoning in research
According to Piaget’s theory of intellectual development, HD reasoning appears in the formal operational stage (Inhelder & Piaget, 1958). Lawson et al. (2000) claim that there are two general developmentally-based levels of hypothesis-testing skill. The first level involves skills associated with testing hypotheses about observable causal agents; the second involves testing hypotheses about unobservable entities. The ability to test alternative explanations involving unseen theoreticalentities is a fifth stage of intellectual developmentthat goes beyond Piaget’s four stages.
II. Simplified examples of hypothetical-deductive reasoning
1. Question ID: 20500121100 and 20500122100
A student put a drop of blood on a microscope slide and then looked at the blood under a microscope. As you can see in the diagram below, the magnified red blood cells look like little round balls. After adding a few drops of salt water to the drop of blood, the student noticed that the cells appeared to become smaller.
This observation raises an interesting question: Why do the red blood cells appear smaller? Here are two possible explanations:
- Salt ions (Na+ and Cl-) push on the cell membranes and make the cells appear smaller.
- Water molecules are attracted to the salt ions so the water molecules move out of the cells and leave the cells smaller.
To test these explanations, the student used some salt water, a very accurate weighing device, and some water-filled plastic bags, and assumed the plastic behaves just like red-blood-cell membranes. The experiment involved carefully weighing a water-filled bag in a salt solution for ten minutes and then reweighing the bag.
What result of the experiment would best show that explanation I is probably wrong?
A. the bag loses weight
B. the bag weighs the same
C. the bag appears smaller
What result of the experiment would best show that explanation II is probably wrong?
A. the bag loses weight
B. the bag weighs the same
C. the bag appears smaller
This question gives students two alternative hypotheses and the experiment to test these two hypotheses. Students need to make a prediction about the results of the experiment according to each hypothesis and consider what result could confirm or disconfirm the hypothesis.
If hypothesis I is right, then the weight of the bag won't change because there are no molecules or ions coming into or going out of the bag. If hypothesis II is right, the bag will lose weight because water molecules move out of the bag. From HD reasoning, we know the answers are A and B.
2. Question ID: 20500221101 and 20500222101
The figure below shows a drinking glass and a burning birthday candle stuck in a small piece of clay standing in a pan of water. When the glass is turned upside down, put over the candle, and placed in the water, the candle quickly goes out and water rushes up into the glass (as shown on the right).
This observation raises an interesting question: Why does the water rush up into the glass?
Here is a possible explanation. The flame converts oxygen into carbon dioxide. Because oxygen does not dissolve rapidly into water but carbon dioxide does, the newly-formed carbon dioxide dissolves rapidly into the water, lowering the air pressure inside the glass.
Suppose you have the materials mentioned above plus some matches and some dry ice (dry ice is frozen carbon dioxide). Using some or all of the materials, how could you test this possible explanation?
- Saturate the water with carbon dioxide and redo the experiment noting the amount of water rise.
- The water rises because oxygen is consumed, so redo the experiment in exactly the same way to show water rise due to oxygen loss.
- Conduct a controlled experiment varying only the number of candles to see if that makes a difference.
- Redo the experiment, but make sure it is controlled by holding all independent variables constant; then measure the amount of water rise.
What result of your test (mentioned in the previous question) would show that your explanation is probably right?
- The water rises the same as it did before.
- The water rises less than it did before.
- The water rises more than it did before.
This question tells students the hypothesis. Students need to design an experiment to check the hypothesis, make prediction about the results of the experiment according to the hypothesis, and consider what result could confirm the hypothesis. If the hypothesis is right, water saturated with carbon dioxide will not absorb as much carbon dioxide from the flame, so the air pressure will not be as low as it was before and the water will not rise as much.
III. Importance of hypothetical-deductive reasoning
1. The importance of hypothetical-deductive in learning
HD reasoning is important in concept construction because students typically do not come to the learning situation as blank slates. Rather, they come with alternative conceptions (i.e., hypotheses) that must be modified or replaced by scientific conceptions. Thus, concept construction often engages hypothetical-deductive reasoning skills (cf. Lawson, Abraham, & Renner, 1989; Lawson & Renner, 1975; Lawson & Thompson, 1988; Lawson & Weser, 1990; Lawson et al., 2000).
Through HD reasoning and experimentation, students can test their preconceptions against scientific concepts and find out which match experimental results. This promotes conceptual change.
2. The importance of hypothetical-deductive reasoning in society
HD reasoning could be useful in everyday life. Here is an example:
- Suppose your portable music player fails to switch on. You might consider the hypothesis that perhaps the batteries are dead. You decide to test whether this is true.
- Given this hypothesis, you predict that the music player should work properly if you replace the batteries with new ones.
- You proceed to replace the batteries, which is the "experiment" for testing the prediction.
- If the player works again, then your hypothesis is confirmed, and you throw away the old batteries. If the player still does not work, the prediction was false, and the hypothesis is disconfirmed. You might reject your original hypothesis and come up with an alternative one to test, such as the batteries are fine but your music player is broken.
This example illustrates the use ofHD reasoning in everyday life, and it is easy to list other examples like this one.
IV. Research on hypothetical-deductive reasoning
Richard J. Bady. Students' understanding of the logic of hypothesis testing. Journal of Research in Science Teaching. Volume 16, Issue 1, pages 61–65, January 1979
Christine Howe, Andy Tolmie. Computer support for learning in collaborative contexts: prompted hypothesis testing in physics. Computers & Education, Volume 30, Issues 3-4, April-May 1998, Pages 223-235
Anton E. Lawson, Brian Clark, Erin Cramer-Meldrum, Kathleen A. Falconer, Jeffrey M. Sequist, Yong-Ju Kwon. Development of Scientific Reasoning in College Biology: Do Two Levels of General Hypothesis-Testing Skills Exist? Journal of Research in Science Teaching, Volume 37, Issue 1, pages 81–101, January 2000
Anton E. Lawson Nicole Drake Jennifer Johnson Yong-Ju Kwon Christopher Scarpone. How Good Are Students at Testing Alternative Explanations of Unseen Entities? The American Biology Teacher 62(4):249-255. 2000
David Moshman, Pat A. Thompson. Hypothesis testing in students: Sequences, stages, and instructional strategies. Journal of Research in Science Teaching, Volume 18, Issue 4, pages 341–352, July 1981
Barbara A. Spellman. Hypothesis Testing: Strategy Selection for Generalising versus Limiting Hypotheses. Thinking & Reasoning, 1464-0708, Volume 5, Issue 1, 1999, Pages 67 – 92
C. dell'Aquila; M. di Gennaro; V. Picciarelli. The logic of hypothesis testing and the control of variables formal schema: Is there a link? International Journal of Science Education, 1464-5289, Volume 7, Issue 1, 1985, Pages 67 – 72