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Scientific Investigation Skills

Stereotypes About Scientists

Many people think scientists are people like Einstein, who had crazy hair and developed explanations about the universe that can be difficult for the average person to understand. Other people think scientists are like characters they see in movies or on television—either glamorous or geeky. Very few people who are not professional scientists think of themselves as scientists. However, the truth is that most people do science or engage in scientific thought every day!

Scientific Questions

Science is a way of learning about the world by asking questions and searching for answers to those questions by gathering evidence, either through observation or through methodical testing.

We ask questions because:

  1. We are curious — "What is that purple plant growing in the school garden?"
  2. The answers influence our lives — "How will climate change affect the planet as I grow up?"
  3. We want to improve the world around us — "How can we increase the nutritional quality of the lunches served at school?"

Many of the questions we ask are directly relevant to our daily lives. For example, people ask questions like "How much electricity does my refrigerator use?" This question could be answered by monitoring electricity use when the refrigerator is plugged in and also when it is unplugged, without changing other electrical use. By comparing electricity use when the refrigerator is plugged in to when it is not plugged in, the electricity use of the refrigerator can be determined indirectly. Tools, such as a wattmeter, can also be used to directly measure the amount of electricity the refrigerator uses.

Language of Scientific Ideas: Opinions, Hypotheses, and Theories

The scientific process involves observing, describing, identifying, testing, and evaluating problems to be answered. As scientists develop ideas and test questions, there are many ways for them to express their thoughts and ideas. Some major categories of expression are: (1) opinions, (2) hypotheses, and (3) theories. In science, these words have specific meanings that may be different than those used in day-to-day conversation. Table 1.1 summarizes these categories of scientific language questions to ask when classifying scientific language.

A hypothesis is a statement that is usually based on observations or evidence. Hypotheses must be testable, and once tested, they can be supported by evidence. Some people refer to a hypothesis as an educated guess, but most hypotheses are more than guesses because they have reasoning behind them. Hypotheses are sometimes expressed in three parts: if, then, and because. A hypothesis can be stated as "If we expose fish eggs to caffeine then they will hatch early because caffeine is a stimulant". In this example, the reasoning behind the hypothesis is in the "because" part of the statement. Hypotheses should be worded so that they can be tested. In the previous example, the hypothesis could be tested by exposing fish eggs to caffeine. Hypotheses are not proven, only supported or unsupported. If the eggs do not hatch early, the hypothesis is unsupported. However, if the eggs do hatch early our hypothesis is supported.

An opinion is a statement describing a personal belief or thought. Opinions cannot be scientifically disproved. Opinions often contain language that describes or compares items in a way that is not measurable as written, such as "bad," "nice," or "better." For example, the statement "the favorite food of hermit crabs is fish" is an opinion. This statement is not testable because 1) it would be impossible to provide everything single food option to every single hermit crab and find out which food is their favorite, and 2) you cannot ask hermit crabs what their favorite food is. However, a critically thinking person can modify an opinion to make it testable and then develop a hypothesis. In the pervious statement, you can change the word "favorite" to "preference," limit the food choices, and identify the type of hermit crab you are interested in studying. A hypothesis would be "the hermit crab Calcinus seurati prefers canned tuna fish to canned clams." This is a testable hypothesis because you can conduct an experiment to see which of these two foods Calcinus seurati will eat more of when given both options. The hermit crab would be said to prefer the food it consumed more of. Scientists would not use the term "favorite" because favorite implies emotion and the knowledge of choices, neither of which are appropriate to hermit crabs.

A theory is a well-substantiated explanation of some aspect of the natural world, backed by evidence, including supported hypotheses. A theory has been evaluated by the scientific community and is strongly supported. One individual cannot come up with a scientific theory. Scientific theories are reserved for big ideas that often describe a large set of observations, and provide a cohesive explanation for those observations. In day-to-day conversation, people may describe ideas as being true or false, but in science, theories are not accepted as true or right. Rather, in science, theories are accepted as the best-supported explanation of the world based on evidence. Sometimes testing reveals that a theory has exceptions, in which case the theory can be modified. One of the hallmarks of science is that ideas can change based on evidence. The theory of evolution by natural selection describes how species change over time in response to environmental conditions. The current theory of evolution has been modified as our understanding of genetics and the inheritance of DNA has advanced.

Table 1.1. Summary of scientific language and questions to ask when classifying scientific language.



Questions to Ask


Personal belief that is not objective, tested, or testable as stated.

Is this a personal belief?


If yes a OPINION


A statement that is testable, offers a possible explanation, and is based on observations about the natural world.

Is this scientifically testable?




A suggested explanation for a phenomenon in the natural world that is well supported by facts, tested hypotheses, and scientific laws.

Is this supported by scientific evidence?


Does it offer an explanation of natural phenomena?


If yes a THEORY

Scientific Explanations

Science is self-correcting and scientific knowledge is constantly being updated. With the introduction of new data, hypotheses and theories can be altered. Unlike opinions, which can change based on the emotions or beliefs of a person or group of people, any changes in scientific ideas must be substantiated by new evidence.

There are many ways to approach a question, but the scientific approach to questioning requires testing through the gathering of evidence. There are some questions science cannot answer, because they are not testable. Questions such as "Why are we here?" or "What happens when we die?" are questions that philosophers and theologians attempt to answer, but these questions cannot be tested by scientists, and therefore are not appropriate questions for scientists to answer.

Supernatural explanations, such as ghosts or magic, are considered unscientific because they rely on a lack of evidence. These explanations cannot be tested, because they are not directly observable. It is easier and more practical to test observable events, because once disproved, these explanations can be eliminated. To support a supernatural explanation, every other possible solution must be tested and eliminated. The impracticality of this task means that it can never be said with certainty that a supernatural explanation explains natural events. For example, attributing a flickering light to a ghost cannot be done with certainty unless every other possible explanation can be disproven, including bad wiring, an old light bulb, power surges in the electrical grid, and more.


Activity: Scientific Language–Opinions, Hypotheses, and Theories

Identify different types of statements as opinions, hypotheses, or theories.

Language of Scientific Ideas: Facts and Laws

In addition to opinions, hypotheses, and theories, scientific ideas can also be classified as facts and laws.

A fact is an observation that has been repeatedly confirmed. Scientists use the word fact to indicate that something has been tested and observed to the point that it no longer needs to be tested. For example, it is a fact that, when observed from above the North Pole, the earth rotates in a counter-clockwise direction. This observation has been confirmed repeatedly, both from earth and space. Scientists no longer need to study this phenomenon to understand it to be true. Facts can drive hypothesis formation, and facts can be used to support laws and theories. However, even though facts are relatively stable, it is important to recognize that new evidence can still disprove ideas that are considered to be facts. For example, in 1795, a kilogram was defined by the weight of a liter of water. Now, a kilogram is defined to be equal to the weight of a standard metal cylinder stored in France. Other scientific definitions accepted as fact have changed over time. For example, the accepted definitions of planet and species, changed as scientists learned more about solar systems and the genetic makeup of organisms.

A law is a specific description of events that will occur under particular circumstances. A law will hold true under specified conditions and can be used to make predictions under those conditions. For example, through careful observation and experimentation, scientists noticed that matter is never lost or gained in chemical reactions. This, and other observations, is formalized in the Law of Conservation of Mass, which states that atoms are the basic particles of matter and that they are not created or destroyed, but instead they are rearranged in chemical reactions. Laws are sometimes expressed as equations using mathematics. Laws are not explanations of occurrences, but are descriptions or predictions of occurrences based on theoretical information. Theories explain why laws hold true. Table 1.2 describes all of the classifications of scientific ideas described in this and the previous section.

Table 1.3. Definitions of fact and law and questions to ask when classifying scientific language.
  Definition Questions to Ask
Fact An objective and confirmed observation about the natural world.

Is this an observation of the natural world rather than an explanation?


If yes → FACT


Law An analytical statement that allows a scientist to make a prediction about how the natural world will behave under a given set of circumstances.

Can this be used to predict how a system will behave under different conditions?


Is there a mathematical equation associated with this?


If yes → LAW



Activity: Scientific Language–Facts and Laws

Identify different types of statements as facts and laws.


Activity: Identifying Opinions, Facts, Hypotheses, Laws and Theories

Identify opinions, facts, hypotheses, laws, and theories in a passage about plate tectonics.

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Exploring Our Fluid Earth, a product of the Curriculum Research & Development Group (CRDG), College of Education. University of Hawaii, 2011. This document may be freely reproduced and distributed for non-profit educational purposes.