Why did Pavlov call his learned response a conditional reflex?

Ivan Pavlov used the term "conditional reflex" because the animal's ability to elicit a specific response—such as salivation—to a stimulus like a metronome is conditional upon a particular set of experiences.1

In his experiments, Pavlov distinguished between two types of stimuli and responses:

• Unconditional: The food is an unconditional stimulus because it invariably elicits salivation, which is an unconditional response.1
• Conditional: The metronome serves as a conditional stimulus. Its power to trigger salivation is not innate but depends on the animal having previously associated the sound with the delivery of food.1

While the term is commonly translated as "conditioned" in English, Pavlov originally used "conditional" to emphasize that the reflex depends on specific environmental conditions and associative learning.12