What characterizes a fallible sign?

A fallible sign is characterized by having more than one possible cause, meaning that while a certain effect might suggest a particular cause, it is not definitive or exclusive. This means that the presence of that effect does not guarantee that the specific cause is the true or only explanation. In many instances, there might be alternative explanations or causes that can also lead to the same effect. This characteristic highlights the uncertainty and potential for misinterpretation in reasoning or inferencing based on such signs.

For example, a person feeling cold can be interpreted as having a fever; however, they might also be cold due to being in a chilly environment or wearing insufficient clothing. Therefore, the effect (feeling cold) has multiple potential causes, which is precisely what defines a fallible sign.

The other options relate to different concepts that do not align with the definition of a fallible sign. An effect that is always accompanied by a specific cause lacks the element of uncertainty that characterizes fallible signs. An effect never supported by true evidence indicates a complete lack of validity, while an effect that validates all possible scenarios implies an overreaching certainty that contradicts the notion of fallibility.