Research undertaken to build knowledge and understanding, regardless of its potential applications. The boundary between pure and applied science is fuzzy. Research undertaken in the pure pursuit of knowledge often ends up having useful applications, and research begun with an application in mind often ends up informing our understanding of the natural world more broadly.

In science, a possible outcome of a scientific test based on logically reasoning about a particular scientific idea (i.e., what we would logically expect to observe if a particular idea were true or false). This website generally uses the term expectation in place of prediction. To learn more, visit our misconception on prediction.

In medical studies, a treatment, medicine, or therapy given to study participants that is known to have no therapeutic effect on the condition of interest. Placebos are used in clinical trials because they help control an important variable: whether or not the participants know that they are receiving treatment for a condition. With a placebo, neither the participants receiving an experimental treatment and nor those in the control group know whether they are receiving the treatment. To learn more, visit our side trip Fair tests in the field of medicine.

Phenomenon in which a patient experiences an improvement (or apparent improvement) in a medical condition simply as the result of receiving some sort of treatment — not because of the effectiveness of the treatment itself. Placebo effects are common and can make it difficult to evaluate new medical treatments because even ineffective treatments may appear helpful. To account for the placebo effect, many clinical trials compare a control group receiving a placebo to an experimental group receiving a new treatment. To learn more, visit our side trip Fair tests in the field of medicine.

The study of what science is and how science works. These topics are not ones for which cut-and-dried explanations exist, and the philosophy of science is an area of active debate and investigation. To learn more, visit The philosophy of science.

A method of vetting articles. Articles submitted to a peer-reviewed publication are sent out to several scientists who work in the same field as the paper’s author. Those reviewers provide feedback on the article and tell the editor of the publication whether or not they think the study is of high enough quality to be published. To learn more, visit Scrutinizing science: Peer review.

Principle suggesting that when two explanations fit the observations equally well, a simpler explanation should be preferred over a more complex one. To learn more, visit Competing ideas: Other considerations.