Observation and Inference

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What do you need in order to form a hypothesis? A hypothesis is not just a random guess; it is a prediction bases on some facts, or observations. But a hypothesis is not a proven fact, so it is also based on inference. Inference means drawing conclusions about the things you have observed.

For example, suppose you hear a crash coming from your bedroom. You enter the room to find your window broken and a baseball rolling across the floor. You can infer that someone hit the baseball through your window and broke it. You did not see the incident happen, but you can make a hypothesis based on your inference.

A very important part of scientific thinking—and thinking in general—is the ability to separate observation and inference. Observations are things you have experienced through the senses, by seeing, hearing, tasting, touching, or smelling. An inference is an explanation or interpretation of what you have observed.

Two people can observe the same situation, and if they are careful observers, they can use their observations to come up with facts about the situation that are not subject to opinion. Inference is very different. Inference depends greatly on personal opinion and ideas. Therefore, two people might observe the exact same events, and infer very different things from them. Hypothesis must be tested. For this reason they are not considered to be fact. If hypotheses were based only on observation and not on inference, there would be no need to test them; they would be fact.

Practice: Read the following passage and decide: (a) what observations Inspector Richards made and (b) what inferences were based on each observation.

Murder?

The rain had just stopped. Inspector Richards arrived at the house at 2 p.m. The front door was locked. He pried open the door and went in. Mrs. Williams was lying in bed. She was dead. The bedroom window faced the garden. The window was open and there were several small puddles of water between Mrs. Williams’s bed and the window. The woman was wearing a pearl necklace, and there was a bottle of pills on the night table near the bed. Mr. Williams was out of town on business.

Because Mrs. Williams was still wearing her pearls, robbery could not have been the motive. It was obviously a case of murder. The murderer must have come in through the bedroom window and killed Mrs. Williams. The puddles of water were probably left by his shoes.

a. Observations:

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b. Inference: