Final answer:
The precautionary approach can be invoked when there is potential harm suspected but not proven, often relating to environmental or health measures where scientific certainty is not fully established, emphasizing proactive caution in the face of possible risks.
Step-by-step explanation:
The precautionary approach can be invoked when potential harm is suspected, but not proven. This approach suggests that when the effects of a human activity are poorly understood, we must presume that some level of harm may exist to the environment, and thus must proceed with that activity carefully. It is an ethical and policy principle that expresses the concept that the lack of full scientific certainty as to the harmful effects of an action, policy, or substance is not a reason to postpone measures to prevent environmental degradation if there are credible threats of harm.
In scenarios like the development of new chemicals, potential public health emergencies, or environmental conservation, caution is exercised due to the possible risks and harms that could arise.