Unit 5: Science and Hypothesis

Science, Logic, and Reasoning
What is a Hypothesis?
The Scientific Method
Criteria for Evaluating Hypotheses

Science, Logic, and Reasoning

Units 1-4 dealt with Deductive Logic, where the conclusion follows from the premises with absolute certainty.

Science, however, relies primarily on Inductive Logic. In induction, the premises (our observations) make the conclusion highly probable, but not certain. Science aims to build the best possible explanation for the evidence we have.

Deduction: "All men are mortal. Socrates is a man. Therefore, Socrates is mortal." (Conclusion is 100% certain).
Induction (Science): "Every swan I have ever seen is white. Therefore, all swans are white." (This was believed to be true until black swans were discovered in Australia).

What is a Hypothesis?

Definition: A hypothesis is a proposed explanation for a phenomenon. It is a tentative, testable "educated guess" about how or why something happens.

It is the starting point for all scientific investigation.
A good hypothesis must be testable and falsifiable (we must be able to imagine an experiment that could prove it wrong).
Example: "My car won't start" (Observation). "The battery is dead" (Hypothesis).

The Scientific Method

The scientific method is the process of using hypotheses to understand the world. While shown as a simple list, it is often a complex, cyclical process.

The Steps:

1. Identify the Problem/Observation: Notice a phenomenon that needs explaining (e.g., "Why are the plants in my garden dying?").
2. Form a Hypothesis: Propose a preliminary explanation (e.g., "Hypothesis 1: There is not enough water." or "Hypothesis 2: There is a pest in the soil.").
3. Deduce Testable Consequences: Logically deduce what *must* also be true if the hypothesis is true (e.g., "If H1 is true, then giving the plants more water will make them recover.").
4. Experiment/Test: Conduct an experiment to test the consequence (e.g., Water one group of plants (the test group) but not another (the control group)).
5. Analyze and Conclude:
- If the plants recover, the hypothesis is confirmed (not "proven," but strengthened).
- If the plants still die, the hypothesis is falsified (disproven).
6. Refine and Repeat: If falsified, go back to Step 2 and form a new hypothesis (e.g., "Let's test Hypothesis 2 about the pests.").

Criteria for Evaluating Hypotheses

Often in science, we have multiple hypotheses that all seem to explain the facts. How do we choose the *best* one? We use a set of criteria:

Criterion	Meaning	Example
1. Explanatory Power	How many facts does the hypothesis explain? Does it explain them well?	Newton's theory of gravity explained falling apples, the tides, and the orbits of planets. It had huge explanatory power.
2. Falsifiability/Testability	Is there an experiment that could prove it wrong? If not, it's not a scientific hypothesis.	"The planets are held in their orbits by invisible, undetectable angels." This is unfalsifiable and thus unscientific.
3. Simplicity (Occam's Razor)	"Do not multiply entities beyond necessity." When two theories explain the same facts, the simpler one is usually better.	The "Sun-centered" model of the solar system was much simpler than the complex "Earth-centered" model.
4. Predictive Power	Does the hypothesis predict new facts that we haven't observed yet?	Einstein's theory of relativity predicted that light would bend around stars, which was later observed during an eclipse.
5. Conservatism	How well does the hypothesis fit with other, well-established scientific laws?	A theory claiming a new plant food works is fine. A theory claiming the plant food works by "magic" would be rejected because it violates the laws of physics.