The Process of Science

Core Concepts

Observation and question

Science begins with observation — gathering information with the senses or instruments. Observations can be:

• Qualitative: descriptive, non-numeric ("the seedlings in the shaded tray grew taller and paler").
• Quantitative: measurable and numeric ("the shaded seedlings averaged 14 cm tall").

Good observations lead to focused questions: Why did the shaded seedlings grow taller? The question narrows the problem to something testable.

Hypothesis, prediction, and the "if…then" logic

A hypothesis is a proposed, testable explanation for an observation. Crucially, it must be falsifiable — some possible observation must be able to show it is wrong. "Invisible fairies make plants grow" is not a scientific hypothesis because no test could disprove it.

From a hypothesis you derive a prediction in if–then form: If shaded seedlings grow taller because they stretch toward light, then seedlings grown in complete darkness should also be elongated.

• Hypothesis: why something happens (an explanation).
• Prediction: what you should observe if the hypothesis is true (a testable consequence).

Designing experiments: variables and controls

The gold standard test is a controlled experiment, in which you change one thing and hold everything else constant:

• Independent variable: the factor the researcher deliberately changes (light level).
• Dependent variable: the factor measured to see if it responds (seedling height).
• Control group: the group receiving no treatment or a standard one, providing a baseline (seedlings at normal light).
• Experimental group: the group receiving the treatment being tested.
• Constants: all other conditions kept identical between groups (soil, water, pot size, temperature).

Why controls matter: without a control group, you cannot tell whether the effect came from your treatment or from an unmeasured factor. In a drug trial, the control group gets a placebo — identical looking but inactive — so the expectation of improvement is not mistaken for the drug's effect.

Reasoning: induction and deduction

• Inductive reasoning draws a general conclusion from specific observations: Every swan I have seen is white → all swans are white. Induction generates hypotheses but can be overturned by a single counterexample (black swans exist).
• Deductive reasoning applies a general principle to a specific case: All mammals have hair; whales are mammals; therefore whales have hair. Deduction powers the if–then step of hypothesis testing.

Science uses both: induction to form hypotheses from patterns, deduction to derive testable predictions from them.

Theories, laws, and the limits of science

A scientific theory is not a guess — it is a well-tested, widely supported explanation integrating many observations and hypotheses (evolutionary theory, germ theory of disease). A scientific law describes a pattern that holds under stated conditions (e.g., thermodynamics) but does not always explain why.

Science has honest limits: it studies the natural world and cannot test supernatural explanations, moral values, or aesthetic judgments.

Worked Example: Does Fertilizer X Help Tomato Plants?

A gardener claims Fertilizer X makes tomatoes grow bigger. Here is how a scientist would test it:

1. Observation/question: Tomatoes in one corner of the garden looked larger after Fertilizer X was used. Does Fertilizer X increase tomato yield?
2. Hypothesis: Fertilizer X increases tomato fruit mass by supplying extra nutrients.
3. Prediction: If Fertilizer X works, then plants treated with it should produce heavier fruit than untreated plants under the same conditions.
4. Experiment: 40 tomato plants of the same variety, soil, pots, water, light, and temperature. 20 get Fertilizer X (experimental group); 20 get none (control group). Fertilizer dose is the independent variable; total fruit mass per plant after 8 weeks is the dependent variable.
5. Result: treated plants averaged 1.9 kg of fruit; control plants averaged 1.2 kg.
6. Interpretation: the result supports the hypothesis — but one trial, one variety, and one site cannot prove it generally. Replication and peer review move a finding toward established knowledge.

Notice what the control group did: without it, you could not rule out that the tomatoes grew because of better weather, not the fertilizer.

Common Confusions