Crusius, Christian August: Road to certainty and reliability – Experience

Crusius sets out as the aim of the practical part of his logic to show how to apply the capacities of understanding for knowing the truth. In order to do this, he explains, we must investigate, on the one hand, sensations or experiences, and on the other hand, judicious use of abstract ideas (memory and ingenuity, he thinks, require no rules). Starting from experience, Crusius notes that the word can refer to two things: to a certain kind of proposition and to an act of experiencing. He mostly deals with the propositions of experience, having only few things to say about the act of experiencing, and I will also focus on the former.

As a proposition, Crusius continues, experience means an immediately sensed connection of subject and predicate. Depending on the kind of sensation, the experience can then be either external or internal. Crusius underlines that internal experience should not be confused with axioms or immediate propositions. We are conscious of all propositions through internal sensation, he explains, but only such propositions are axioms, where we immediately sense an essential connection between the subject and the predicate, so that when the predicate is denied, the concept of subject must also disappear. On the other hand, a mere internal experience is a proposition where the subject and the predicate are internally sensed as existentially connected.

Although it would be natural to assume that in all experiences both the subject and the predicate would have to be sensuous, that is, ideas generated through sensation, without the aid of any abstraction, Crusius notes that we can sense also a mere existential connection of such objects that are thought through abstract ideas. Thus, he divides experiences into common and reflecting experience, based on whether the subject and the predicate of the experience are sensuous or abstract.

Crusius states that the certainty of the propositions of experience are shown by his earlier demonstrations about the certainty of our sensations. Of course, he adds, it is still a possibility that what we think is a proposition of experience contains something else, for instance, imaginations and even outright impossibilities, connected to obscure and incomplete sensations. Thus, Crusius concludes, we need some rules to decide when we have a true proposition of experience in front of us. Thus, while experience teaches us that in certain circumstances certain representations are generated in us, a proposition stating that something existing is connected with these representations is already dependent on further deduction. Other clear instances of propositions that cannot be propositions of experience, according to Crusius, are negative propositions (experience can only tell that we do not sense something), causal propositions (experience can only show connections between representations) and universal propositions (abstractions cannot be sensed as abstractions).

Crusius continues by noting that, according to experience, we do not sense simple substances nor their fundamental forces. This means, he explains, that we cannot sense the fundamental essence of anything, since things are divided into abstractions, simple substances and complex substances, out of which we can sense only the last one, and even in their case we cannot sense how they consist of simple substances, which we would have to do, in order to sense their essence. Many of seeming propositions of experience, Crusius concludes, are then only mixed experiences, that is, they require something added to sensations through proofs.

Hoffmann: Study of reason – Learning from experience

While the first part of Hoffmann's grand work studied theoretical underpinnings of knowing truth, second part should deal with the difficult task of finding truth in practice. This involves going through questions already dealt in the first book, but from a different perspective. For instance, in the first book we learned to classify ideas according to various criteria, such as their sources and their relations to one another. In the second book, Hoffmann wants to merely how to achieve ideas that can be used for acheiving truth.

Now, an important precondition for achieving truth is to have ideas at all – no ideas, no knowing truth. Furthermore, the primary and in a sense first source of ideas is sensation or experience, which also connects ideas with things. Thus, a precondition for knowing truth, Hoffmann says, is to have reliable experiences of things and especially avoid any possible mistakes in experience, reasons for which Hoffmann goes on to enumerate – we might think we have experienced something, which we haven't actually experienced, our experience of something might be lacking in details etc.

Of these reasons, the most important is the first – some things really are beyond the ken of our experience and cannot thus be justified through experience. We have already seen that the truth of experience itself is something that cannot be experienced, but must be justified through some further arguments. Similarly, we cannot really justify through mere experience that what we experience has just the properties we experience it to have. Thus, a Leibnizian, who denied that external things had any influence on our soul, could not say that the world existed in the manner that our sensations appeared to suggest – and not even that there was any world outside ourselves to speak of.

Furthermore, there are plenty of other things that we cannot directly sense, like future events and infinite collections of things, which prevent us from basing universal propositions on mere experience. In addition, because we cannot observe things that haven't really happened, but might have happened, we cannot draw contrafactual conclusions from mere experiences – e.g. we cannot say on the basis of mere experience that someone would have dies, if she would not have taken a medicine.

A further important question for Hoffmann was to decide what sensations and experiences to choose as basis of further investigation, since clearly one could not consider everything one sensed. Here Hoffmann emphasises the role of experimentation. One should not just go on perceiving things randomly, but e.g. make a preliminary hypothesis and see whether it fits what we perceive. Furthermore, in case of complicated questions one should divide the problem into several subproblems, in order to make it easier to find the important observations. This is not to say, Hoffmann admits, that controlled experiments are the only worthy way to experience and that mere observation is of no consequence. On the contrary, it might well be that such observations reveal some unexpected facts that could not have been discovered through tightly controlled experiments.

Such is Hoffmann's short investigation of the intricacies of experience. Next in the progress of methodology, Hoffmann considers definitions.