What is exercising me at the moment is the question of how suspending judgment as to the truth or falsity of a proposition p is related to presuming that p. I will propose that there are two forms of suspension of judgment. There is suspension in the service of cognition and suspension in the service of ataraxia (mental tranquillity). I will float the suggestion that presumption necessarily involves suspension in the service of cognition but excludes suspension in the service of ataraxia.
Firearms instructors sometimes say that every gun is loaded. That is plainly false as a statement of fact, but a wise saying nonetheless if interpreted to mean: every gun is to be presumed loaded until proven unloaded. Note that it makes no sense to say that a gun is loaded until proven unloaded. For it it is loaded, then it cannot be proven to be unloaded. Likewise, it makes no sense to say a man is innocent until proven guilty; for if he is innocent, then he cannot be proven guilty. A man charged with a crime is presumed to be innocent; a gun is presumed to be unloaded.
Presumptions are procedural rules. To presume every gun to be loaded is to adopt a procedural rule to treat every gun as if it is loaded regardless of how likely it is that it is loaded. Suppose the likelihood is near zero: the gun is 'right out of the box' or is placed on the counter by a responsible gun dealer. Nevertheless, the presumption that it is loaded remains in force.
Suppose the likelihood is not near zero but is zero: I remove the magazine of a semi-auto pistol and do both a visual and tactile check of the chamber. The chamber is empty. I now know -- hyperbolic doubt aside -- that the gun is unloaded. The presumption that the gun is loaded has now been defeated. I will assume that all presumptions are defeasible.
Presumption is not belief. If I presume a gun to be loaded, I do not thereby believe that it is loaded, or affirm or accept or assert that it is loaded.
To presume that p is not to affirm that p is true, nor to affirm that p is probably true, nor to assume that p is true, but to decide to act as if p is true. When I presume that a gun is loaded I do not affirm that it is loaded, deny that it is loaded, take a position on the probability of its being loaded, or even assume that it is loaded. Assumption is a theoretical attitude toward a proposition. My mental attitude of presumption is not theoretical but practical: I decide to comport myself as if the gun is loaded.
A presumption is not like a belief in the following important respect. To presume that a gun is loaded or that a man is innocent of a crime is not to believe that it is or that he is. To believe that p is to believe that p is true. But to presume that p is not to presume that p is true; it is to act as if p is true without either accepting or rejecting p. To presume that Jones is innocent until proven guilty is not to believe that he is innocent until proven guilty; it is to suspend judgment as to guilt or innocence until sufficient evidence is presented by the prosecution to warrant a verdict one way or the other. When I presume that p, I take no stand as to the truth-value of p, or even the probability of p -- I neither accept nor reject p -- what I do is decide to act as if p is true.
Two Forms of Suspension of Judgment
To presume that a gun is loaded until proven unloaded is not to believe that the gun is loaded until proven unloaded; it is to suspend judgment as to whether it is loaded or unloaded until a decision can be made on the basis of empirical evidence. The suspension in this example is pro tempore and is in the service of getting at the truth. This form of presumption necessarily involves suspension of judgment at least for a time.
But suppose I suspend judgment from a state of evidential equipoise. I am in a state of evidential equipoise when it appears to me that the evidence for a thesis T and the evidence for its negation ~T are equal: the considerations on either side of the question balance and cancel out. Suppose I now move from a state of evidential equipoise to a state of suspension of judgment. Before suspension I was in a state of inquiry and mental turmoil trying to resolve a seemingly important question. But then, seeing that there is no rational resolution of the question -- say, whether or not justice demands capital punishment in some cases -- I enter upon the state of suspension. There follows ataraxia and the removal of mental turmoil, both within my own mind, and with intellectual opponents. This peace of mind is not the "peace that surpasses all understanding," (Phillipians 4:7) but an arguably paltry peace that comes from acquiescing in a failure of understanding. I give up up the search for the truth of the matter. Inquiry having led me to an impasse, I abandon inquiry and cease troubling my head over an apparently insoluble problem.
So we have two forms of suspension of judgment. The first form is for the time being and is oriented toward uncovering the truth of the matter. Is the gun loaded or not? Is the defendant guilty as charged? The suspension ends when a verdict has been reached. The second form remains in place once evidential equipoise is reached. The suspension is not for the sake of inquiry into the truth, but for the sake of mental calm. Inquiry issues in the abandonment of inquiry. Suspension in its second form has nothing to do with presumption.