How did the Russian term “conditional reflex” become “conditioned reflex” in English?

The Russian term for Ivan Pavlov’s discovery is accurately translated as "conditional reflex," reflecting the idea that the reflex is conditional upon specific experiences. However, during the translation of his work into English, the terms "conditional" and "unconditional" were commonly, though incorrectly, rendered as "conditioned" and "unconditioned".12

This shift in terminology became standard in English-language scientific literature, leading to the widespread use of "conditioned reflex" and the subsequent introduction of the verb "to condition" to describe the experimental process.2