Latin Scientific Phrases A Priori, A Posteriori, and Ad Hoc

When translating from Latin to English, there is a difference between literal translations and those that convey a metaphoric meaning that include more information than the phrase’s literal meaning. Often, a Latin phrase has become so common that its literal meaning is no longer considered the phrase’s actual translation.

A Brief Description of Empirical Research

Empirical research is any scientific study in which experience, observation, or data is used to test hypotheses about phenomena. This is in contrast to theoretical research in which the scientist philosophizes about the relationships among variables. The field of philosophy of science sets forth laws or rules to which scientists must adhere to be certain that variables outside the study have not caused or influenced the relationships among the variables.

To communicate to the scientific community that these rules are followed, researchers often use Latin phrases to indicate which philosophies of science the scientist has used conducting a research program. One of these philosophies is that in which the scientist has hypothesized the relationships among variables, before confirming those relationships with observations or data. These deductive methods increase the likelihood that the relationships are true and are not an artifact of the data. So-called inductive methods are those where a researcher examines data in order to discover relationships among variables. In doing so, the researcher discovers relationships that are difficult to predict but does so at the cost of external validity – the assumption that the same relationships are observable in subsequent data.

Latin Phrases in Empirical Research

Latin, the former official language of science from previous centuries, lingers in today’s scientific community as a throwback to the earlier days of modern science. Throughout the last few centuries, Latin has been associated with the learned, universities, and the church. Even today, Latin still carries with it an air of sophistication and refinement.

The Latin phrase “a priori” is so prevalent in the English that it even appears in its unaltered form in most dictionaries. An appropriate literal translation is “from the former” and is used when a researcher has specified relationships among variables – or hypotheses – without the benefit of data. By specifying hypotheses a priori, the researcher has increased the validity of the relationships because he/she has reduced the chances that the relationships are specific to one sample of data rather than generalizable to other samples or populations.

The Latin phrase “a posteriori”, also found in an English dictionary, can be appropriately translated as “from the latter.” This phrase is used to indicate that hypotheses are the result of observation or data from which the relationships were derived. Although the external validity of such hypotheses are much lower than in an a priori specification, a posteriori methods do allow for the discovery of relationships that would have been difficult, if not impossible, to predict without the benefit of data.

Often, the phrase “ad hoc” is used when a posteriori is more appropriate. Ad hoc, translated literally as “for this [purpose]”, is used when a researcher wants to convey that findings resulted from the benefit of data. Although similar to a posteriori, ad hoc analysis help explain failed support for a priori hypotheses, not as the main method driving the research. Ad hoc analysis are often exploratory in nature and are used to push knowledge forward in an otherwise a priori study to point future research in a new directions, explain phenomena that could not be explained by the a priori method, or explore unconventional relationships not warranted by a priori specification.


The three Latin phrases discussed above are commonly found in scientific papers, especially in the social sciences such as social psychology, sociology, and management. Often, researchers themselves will confuse the three and assume they are conducting a priori research when they are really conducting a posteriori. Such mistakes give false impressions to other researchers about the validity of a study. Perhaps as Latin continues to diminish as the language of science, researchers will begin using vernacular to describe their research programs to avoid such ambiguities in using a language understood by so few.