§31. Nominal Causality
Things can be really related (true relational propositions) without relations being real things. Ockham argues along similar lines that while there are true propositions of cause and effect, no causality connects absolute relata.
Having reduced being to individuals, no real thing participates in the nature of any other, and no knowledge however perfect of one being discovers knowledge of another. Analyze the cause as closely as you can, you never find the effect in it. All we know of causality is that when one given thing is present, another, which we call the effect, is habitually observed to follow. “The definition of the efficient cause is, to be that whose existence or presence is followed by something else.” To be the cause of an effect “is nothing else than that the effect exists at the presence of the thing.” He disallows inference from creatures to their cause, canceling the cosmological proof of God, and disallows final causes—“This movement towards an end is not real but metaphorical,” which scotches the teleological proof.57Ockham pronounces as self-evident both the principle of causality— whatever has a beginning has a cause—and the principle that like causes have like effects. However, no specific causal generalization is logically evident per se, and a demonstrative science of causes on the model of Aristotle’s Posterior Analytics is not possible. “Although it is incompatible with what Aristotle says, in truth no proposition made up of terms introducing corruptible things only, and that is merely affirmative, categorical, and present-tense, can be the principle or conclusion of a demonstration, because any proposition of this sort is contingent.” Science, such as it is, reduces to perceptual knowledge of existence—fallible, hypothetical correlations verified by experience or experiment (synonymous in Ockham’s time).
He does not regard experimental cognition as problematic. It is not Aristotelian demonstration, and thus not scientia, but it is the best natural knowledge can achieve, and its logic can be respectably formalized.58Aristotle’s epagoge was an inexplicable power of nous to discern principles amid the desultory data of experience. With Ockham it becomes a logical method, a use of signs. Experimental induction is a species of formal consequence which, unlike a syllogism, requires an extra-logical connection among its terms, which Ockham finds in the principle of the uniformity of nature. The reasoning arrives at evident knowledge, and its effects are not different from those of full-dress demonstration, yet it is a far-reaching departure from Aristotle. Ockham discovers continuity between the fallible knowledge of experience and accomplished science. Ars and scientia do not replicate the dichotomy classical philosophy inserted between techne and episteme. Experience can do as well as deduction; for neither does well in natural philosophy. Knowledge of nature cannot be unconditionally certain, because the contingency of nature implies that effects can be produced by multiple naturally possible lines of causation. We can make sagacious conjectures, but “it is impossible to demonstrate that anything is a cause.” Emphasis falls on demonstrate. He is not saying that we cannot have error- free knowledge about causes and effects, but that we cannot demonstrate such propositions as scientia-knowledge strictly requires. Ultimately, the reason is God's power: “God is a free cause in relation to any effect,” a conclusion Ockham and others drew from the condemnations of 1277.59
Aristotle excluded the plurality of causes, where the same effect might have more than one cause. He was followed by Grosseteste and Thomas Aquinas but not Ockham, who tolerates the plurality of causes much as Epicurus did a plurality of causal explanations. Simple knowledge of anything never leads to knowledge of another.
“However often one experiences in himself that he knows something perfectly and intuitively, he never knows something else by means of this knowledge unless he previously also had knowledge of that other thing.” If we could observe a single case of A causing B, we could, with the principle of uniformity, infer that A causes B. But we would have to be sure that we really did observe A cause B, which requires that we eliminate all other possibilities, and that cannot be done. Causation is therefore never provable to a certainty. Is it surprising that Ockham's example comes from medicine?In most cases a singular contingent proposition cannot be known evidently without many apprehensions of single instances, whence it is not easy to know that this herb cured a certain invalid and that it was not the doctor who cured him. And so with many other cases, for it is not easy to grasp that which is experienced, because the same species of effect can exist through many specifically different causes.
An uncertain penumbra surrounds natural knowledge, though methodical experiments can eliminate alternative causes case by case, and rules are defined for verifying causes and effects; for instance, Ockham’s early statement of J. S. Mill’s Method of Agreement and Disagreement:
This is sufficient for anything being an immediate cause, namely, that when it is present the effect follows and when not present, all other conditions being the same, the effect does not follow.... That this is sufficient for anything to be an immediate cause is clear because if not, there is no way of knowing that something is an immediate cause of something else.............................................................................. All
causes properly so-called are immediate causes.
He gives an example, again from medicine. Suppose we generalize that all herbs of such and such a species cure fever:
This cannot be demonstrated by syllogism from better known propositions, but it is known only by intuitive knowledge and perhaps of many instances.
For since he observed that after eating such herbs the fevered person was cured and he removed all other causes of his recovery, he knew evidently that this herb was the cause of recovery, and then he has experimental knowledge of a particular connection.60The justification for the method is desperate—without it, natural knowledge of causes is impossible, therefore it works. A skeptic might draw another conclusion, but Ockham has no patience for skepticism. A scholar writes of his “unshakable conviction in the possibility of certain knowledge and... a natural universe so ordered as to assure that possibility.” You have to have faith if you want knowledge; for example, faith in the principle of nature’s uniformity. The nature and order of experience has no rational ground and cannot be deduced from a principle, but it is secure in God’s immutability.61
Buridan returns to the mystery of epagoge. He posits “a certain innate power in us, naturally inclined and determined to assent to the truth of principles, if they have been properly presented to it, just as fire is naturally inclined to burning when it has been placed next to something combustible.” He says that our intellect, “predisposed by its natural inclination to the truth, assents to the universal principle by experience, and it can be conceded that experiences of this kind are not valid for absolute evidentness, but they are valid for the [kind of] evidentness which suffices for natural science.” This appeal to our good nature is not a mere flourish. He seems genuinely to require and expect a natural response to carry the weight of experimental inference, or what he calls inductio experimentalis. These “draw together (inductio) many particulars, through which the intellect, although it does not see what is immediate or the rationale for what is immediate, is driven by its natural inclination toward the truth to admit a universal proposition.” His conclusion resembles that of Philodemus the Epicurean in its naturalistic optimism. “Although poor and insufficiently examined experiences often lead to error, much experience properly examined in a wide variety of cases never leads to error.”62
Ockham was not an experimenter. Roger Bacon's scientia experimentalis, a science of instruments and operations, would not interest him. “But, in spite of that,” historian of science A. C. Crombie writes, “the effect of his logical and epistemological doctrines was to predispose natural philosophers to seek knowledge of nature by experiment.” He remains an Aristotelian natural philosopher, though he makes the philosophy more consistently empirical than it had ever been. Aristotle insisted that science begins with experience. With Ockham it never attains anything but a wider knowledge of experience, and cannot finally be distinguished from ars or techne.63