# Does the concept of "side-effect" predate functional programming?

When I was reviewing a book, I saw that there's a sentence claiming "side effect is a term coming from the domain of functional programming". I would think that the concept existed before the invention of the functional programming paradigm, but the author is asking for a citation that I was not able to find. Does the concept of "side-effect" actually predate functional programming, or is the author right?

• I have no problem with the concept predating functional programming, it just seems that in order to understand functional programming one must acknowledge what a side effect is, (which the author seems to imply is taken for granted at times in non-functional programming). So the functional programmers use the term (side-effect) to name something that is taken for granted. To me it seems you have two ideas that you think are both apples when you really have an apple (defining a term) and an orange (the existence of a term). Sep 29, 2021 at 10:25
• Drugs have been known to have side-effects for a long, long time. Sep 29, 2021 at 11:59
• @GuyCoder yes, the concept obviously does exist without/before functional programming, but I am curious whether its definition also happened before the invention/definition of functional programming. Sep 29, 2021 at 12:27
• You seem to have fallen into a problem I find often with StackExchange questions. They ask the question in the title, elaborate a bit and end up asking a different question. I.e. Title: Does the concept of "side-effect" predate functional programming? - final question: is the author right? :) If you really want just an answer to a simple question then just ask the simple question without side effects. Pun intended. Sep 29, 2021 at 13:25