The difference between testimony and decidability regarding the satisfaction of the demand for infallibility is operationally clarified as follows:

Testimony:
Operational Role: Testimony is a promise of having performed sufficient due diligence, minimizing involuntary costs imposed upon oneself or others’ demonstrated interests.
Functionality: Testimony serves as evidence of warrantied truthfulness or honesty, subject to conditions of knowledge, language, due diligence (effort in eliminating error, bias, deceit), and contextual precision.
Scope of Infallibility: Testimony doesn’t guarantee absolute infallibility; rather, it promises effort to approach infallibility to the highest achievable standard given limits of human faculties, diligence, and context. In other words, testimony promises a process, not an absolute outcome.

Decidability:
Operational Role: Decidability indicates that the available information has reduced the possible alternatives to improbable or impossible, allowing a choice or statement to be made with minimal risk of imposing involuntary costs.
Functionality: Decidability establishes conditions under which a claim can reliably satisfy the demand for infallibility. It’s a measure of how completely uncertainty has been eliminated or mitigated.
Scope of Infallibility: Decidability doesn’t just promise diligent effort; it asserts that uncertainty is sufficiently reduced such that infallibility (absence of involuntary costs to demonstrated interests) is reliably achieved in the given context. Thus, decidability guarantees an operational outcome (practical infallibility), provided the context is respected.

Summary of Difference:

Testimony is fundamentally a promissory act—an assurance of careful investigation, minimized bias, and diligent effort toward truthfulness.

Decidability is fundamentally a state of affairs—an outcome demonstrating that available information and adversarial testing have sufficiently limited uncertainty, rendering infallibility practically achievable.

In operational terms, testimony provides warranty of method and effort, whereas decidability provides warranty of result or state of completion. Both satisfy the demand for infallibility, but from different perspectives: testimony as promise and method, decidability as proven state of informational sufficiency and reduction of alternatives.