An explanandum (a

Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through ...

term) is a sentence describing a

phenomenon A phenomenon ( : phenomena) is an observable event. The term came into its modern philosophical usage through Immanuel Kant, who contrasted it with the noumenon, which ''cannot'' be directly observed. Kant was heavily influenced by Gottfrie ...

that is to be explained, and the explanans are the sentences adduced as explanations of that phenomenon. For example, one person may pose an ''explanandum'' by asking "Why is there smoke?", and another may provide an ''explanans'' by responding "Because there is a fire". In this example, "smoke" is the ''explanandum'', and "fire" is the ''explanans''.

Carl Gustav Hempel Carl Gustav "Peter" Hempel (January 8, 1905 – November 9, 1997) was a German writer, philosopher, logician, and epistemologist. He was a major figure in logical empiricism, a 20th-century movement in the philosophy of science. He is e ...

and Paul Oppenheim (1948), in their

deductive-nomological model The deductive-nomological model (DN model) of scientific explanation, also known as Hempel's model, the Hempel–Oppenheim model, the Popper–Hempel model, or the covering law model, is a formal view of scientifically answering questions asking, ...

of scientific explanation, motivated the distinction between explanans and explanandum in order to answer why-questions, rather than simply what-questions:

References

Concepts in logic Philosophy of science Linguistics {{science-philo-stub