Predicting the Future: Testable Hypotheses and Scientific Reasoning

Welcome to one of the most exciting parts of being a scientist! Before a scientist starts mixing chemicals or measuring forces, they don't just "see what happens." They make an educated prediction about what might happen. This isn't a random guess—it's a testable hypothesis backed up by scientific reasoning. In this chapter, you will learn how to turn a curious question into a professional scientific prediction that meets the IB MYP Criterion B requirements.

Don't worry if this seems a bit formal at first. Once you learn the "If... then... because..." formula, you'll be able to write hypotheses like a pro!

What is a Testable Hypothesis?

A hypothesis is a specific, trial statement that predicts the relationship between two things: the thing you change (the Independent Variable) and the thing you measure (the Dependent Variable).

To be a "good" hypothesis in the MYP, it must be testable. This means you must be able to perform an experiment to see if your prediction was right or wrong.

Quick Note: For a refresher on identifying variables, see the chapter on "Scientific method, questions and variables."

The Golden Formula: "If... then... because..."

The easiest way to write a high-quality hypothesis is to follow this structure:

If [I change the independent variable in this way], then [this will happen to the dependent variable], because [scientific reason].

Example:

"If the temperature of the water is increased from \(20^{\circ}C\) to \(80^{\circ}C\), then the sugar will dissolve faster, because the water molecules will have more kinetic energy to break down the sugar crystals."

Key Takeaway: A hypothesis is more than a guess; it is a predicted relationship that can be proven or disproven through data.

Adding "The Why": Scientific Reasoning

In MYP Years 3 and 5, simply saying "I think X will happen" isn't enough for a high achievement level. You must explain your prediction using scientific reasoning. This is the "because" part of your statement.

Your reasoning should connect to the scientific topics you are studying, such as:

  • Forces: Using ideas about friction, gravity, or balanced forces.
  • Cells: Using ideas about osmosis, respiration, or cell structures.
  • Matter: Using the particle theory or bonding.
  • Energy: Using the laws of thermodynamics or energy transfer.
Analogy: The Courtroom

Think of yourself as a lawyer. Your prediction is your "opening statement" (what you think happened), but your scientific reasoning is the "evidence" (the scientific laws) that proves your point is logical.

Quick Review: Reasoning answers the question: "Why, according to science, should this happen?"

Making it "Testable" and Specific

A common mistake is being too vague. A hypothesis must be specific enough that someone else could look at it and know exactly what you are measuring.

Bad Hypothesis: "If I give plants more light, they will grow better." (What does "better" mean? Height? Leaf count? Mass?)

Good Hypothesis: "If the light intensity is increased, then the height of the Phaseolus vulgaris (bean plant) will increase, because more light allows for a higher rate of photosynthesis, producing more glucose for growth."

Common Mistakes to Avoid:
  • Using "I think" or "I believe": Science is about objective evidence, not personal feelings. Keep it formal!
  • Forgetting the direction of change: Don't just say the variable will "change." Say it will increase, decrease, or stay the same.
  • Ignoring the "Why": If you leave out the scientific reasoning, you cannot reach the highest marks in Criterion B.

Evaluating the Validity of your Hypothesis (Criterion C)

After you have finished your experiment and collected your data (which you'll learn about in the "Presenting and transforming data" chapter), you must go back to your hypothesis. This is part of Criterion C: Processing and Evaluating.

You need to determine if your hypothesis was:

  1. Supported: Your data matches your prediction perfectly.
  2. Partially Supported: Some data matches, but there are some surprises.
  3. Refuted (Not Supported): The data shows the opposite of what you predicted.

Important: It is perfectly okay in science if your hypothesis is refuted! Some of the greatest discoveries happened because a scientist was wrong and had to figure out why.

Did you know? A hypothesis can never be "proven" 100% true forever; we just say the current evidence "supports" it!

Summary Checklist for Students

When you are writing your hypothesis for an assessment or the eAssessment, check it against this list:

  • Does it start with "If" and mention the Independent Variable?
  • Does it continue with "then" and predict the Dependent Variable?
  • Does it include the word "because" followed by a Scientific Reason?
  • Is it testable? (Can you actually measure it?)
  • Is it specific? (e.g., instead of "speed," use "time in seconds to travel \(5\) meters").

Key Takeaway: The "because" is the bridge between your imagination and real science. Use the concepts you've learned in class (like states of matter or electromagnetism) to build that bridge!