It is not the intention of this website to fully elaborate and defend a Theory of Knowledge. I just explain what I think is the most plausible theory.
We still do not know enough about our own minds and our perceptual apparatus to settle the matter completely. Moreover there are weird and intricate problems about the role of the observer in quantum mechanical experiments.
Whatever the exact nature of our knowledge, when it is to be published, I demand that it be communicable, otherwise it would not make sense to even offer this website.
The most plausible view of knowledge, for the time being, is the REALISTIC VIEW, which means that it is presupposed that there is a reality, that is independent of a knowing subject and independent of being known. Of course our knowledge will be colored by our way of knowing, but this can in principle be accounted for. Accordingly we can in principle know this reality (and the things belonging to it) how it is in itself. The question whether we can know this Reality completely is irrelevant in the present context. The vastness of reality could of course be such that a complete knowledge is beyond our capacity (the capacity of our brains).
In the following we shall describe this realistic view of (human) knowledge.
FIRST INTENTIONS are meanings or concepts derived from, or at least verifiable in, extramental, i.e. real, things, for example the meaning we derive from those things which are human beings, and which (meaning) we denote with the word HUMAN BEING, namely the meaning RATIONAL ANIMAL. The concept HUMAN BEING is an intentional natural sign (denoted with the conventional sign HUMAN BEING -- i.e. with the word HUMAN BEING) of which the content is directly situated in the things themselves (things, existing outside the thinking subject as thinking subject) according to the Realistic View of Knowledge. This extramental content accordingly is what the concept means, and this we denote by RATIONAL ANIMAL. The concepts HUMAN BEING and RATIONAL ANIMAL have the same content, but the latter is the former in an analysed fashion, it is an explanation of the former.
First intentions intend one or another abstract feature in the extramental reality, on the basis of a sensory perception, and this perception is a perception OF (i.e. concerning) extramental reality [and not the ' reality ' of, say, mathematical patterns, because in this case an abstraction process is not needed (See NOTE 1 )].
By the ability to directly intend features of the extramental reality we can in principle going to know things as they are in themselves.
First intentions also can intend individuals existing in this extramental reality. In this case we do not have to do with conceps, but names, like SOCRATES.
SECOND INTENTIONS are meanings, derived from, or verified in, first intentions (or second intentions).
Thus the first intention ANIMAL is a part of the first intention HUMAN BEING (because RATIONAL ANIMAL = HUMAN BEING), and likewise is this first intention ANIMAL also a part of the first intention DOG (because a dog is, just like a human being, also an ANIMAL, although not a rational animal). This relation, found by the intellect, between (first) intentions (in this case the finding that ANIMAL is common in HUMAN BEING and DOG) can be expressed by stating that ANIMAL is a genus of HUMAN BEING and DOG.
GENUS (in the sense of something being a genus, i.e. a genus AS genus) thus is a second intention. So those intentions concerning other intentions (first or second intentions) are second intentions. And these are the logical intentions. Logical intentions are relations the intellect can detect among the many different ways the intellect apprehends extramental things. With the notion of EXTRAMENTAL THINGS I mean things-as-things, in opposition to things-as-known. And the mind can sometimes handle mental things AS IF they are extramental things. In that case the intention of such a mental thing (which is now not an intention itself, but an object) is a first intention.
Second intentions, i.e. logical intentions, only exist in the mind (the intellect). They are characterizations which belong to things-as-known, not to things-as-things.
This cognition-theoretic ' realistic ' view presupposes the presence of abstract features (within things -- of course as such they are not yet abstract[ed]) which can be intended in a direct fashion by first intentions, and because of this direct ' contact ' of the knower (in the sense of the knowing intellect) genuine knowledge is in principle possible.
By pondering about all possible first intentions (the assessment of types of first intentions) like ANIMAL, HUMAN BEING, RATIONAL, their functioning and mutual relations, we will gain insight in the process of knowledge itself, and those findings, we record, as has been said, in second intentions.
This nominalistic view about the nature of knowledge, a view that continues to be held even in our days, contains, according to me, a number of weak points :
That the assumption of the presence, in the extramental material world, BOTH of potentially abstract, i.e. general, features (which consequently can be abstracted from a multitude of individual things), AND (the presence of) concrete things in that same world, is a legitimate assumption, can be illustrated by a consideration of the interdependence of MOTIF and BACKGROUND in whatever world. Let me expound this in NOTE 3 .
So the motif "presence of abstract(able) entities" demands its background "the presence of concrete entities".
And because of this, direct cognitive contact (by means of concepts) with the things to be known is possible.
But one could, while admitting the presence of both mentioned types of entities, assert or assume, that each type resides in a separate domain. Our cognitive mental instruments, the manipulation of concepts and propositions, and the results of these manipulations – knowledge – could then exclusively reside in one domain, while the things to be known reside in the other domain.
Seen in this way, we arrive at a nominalistic view of knowledge, despite the application of the Principle of the Coexistence of Motif and Background.
This, however, is only seemingly so. If we apply the just mentioned Principle, then we must admit that we are talking about one and the same world after all, because "presence of both Motif and Background" implies one world in which they are present. This means that the "extramental world" is not ontologically different from the "mental world". We only distinguish between the two when knowledge is involved, in the sense that (we can say that) "we have knowledge of things other than ourselves".
" That which is not objectively observable does not (objectively) exist, and consequently only exists in dependence on the observer, i.e. only exists subjectively. "
[ Something that is not (objectively) observable could nevertheless exist, because the existence of whatever thing (or state of affairs) does NOT necessarily imply its observability [See NOTE 4 ]. But if something is observable then it must exist. So observability and existence are not equivalent.]
The philosophical assertion, given above, expresses a tendency to involve the observer in the EXISTENCE of things or states of affairs (for example the existence of a certain velocity -- belonging to a certain electron), or a tendency to make the existence of some things, which really are outside the observer, nevertheless dependent on the observer. Of course such a non-(direct or indirect)-observable entity or feature does not as such enjoy existence (and also does not enjoy meaning) WITHIN (the practice of) NATURAL SCIENCE -- so for example the exact position of a subatomic particle within one or another experimental set-up -- because verification of theories of Natural Science must always proceed according to a direct or indirect sensory observation (which often means doing an experiment) [ NOTE 5 ].
But within METAPHYSICS, which is a contemplation in an absolute context, the existence of such a non-(direct ot indirect)-observable thing cannot be denied just on the basis of the fact that it is non-(direct or indirect)-observable (i.e. not objectively observable), because this is an epistemological argument (thus based on observability and knowability), and such an argument cannot, just like that, be valid within Metaphysics, because Metaphysics is an ontological consideration of things (i.e. a consideration within a theory of Being). Arguments within Metaphysics must be of an ontological nature.
Let us summarize all this :
This discussion does not concern the question whether electrons are particles or waves (or a complementary ' marriage ' of these aspects). It concerns the fact that they, whatever else they may be, exist independently of us (independently of our thinking and observing). The subjective aspect, supposed by Quantum Mechanics (better : the interpretation of its experimental results) is an effect of the inadequacy of the models used, models for a more or less complete description of these (submicroscopical) entities [NOTE 6].
The argument -- expressed on the basis of the supposed necessary connection with the observing subject -- that objective knowledge would be impossible, is, when it is based on the quantum mechanical experiment, in any case invalid because of the following reason :
The disturbance, which is, it is true, not completely restorable, and which always pops up in such experiments, or, said differently, the disturbance, produced by that very observation, is NOT a disturbance of the nature of the relevant material entities and does not mean any change of the prevailing lawfulness. These remain as they were, whether they are (by means of an experiment) observed or not. The disturbance only relates to the state in which the (quantum)system happened to be in. Quantum Mechanics teaches us about the general properties, for example those that are present in every Hydrogen atom, it thereby teaches us about the different characteristic energy states of the Hydrogen atom, characteristic for the nature of Hydrogen (i.e. for the nature of every Hydrogen atom). The possibility of knowing this objectively is not denied by Quantum Mechanics. But what Quantum Mechanics also teaches us is that as soon as we try to know something about a certain (determined) state of this or that individual Hydrogen atom, this state (for example its position + momentum) will be changed by the fact of the experiment (the activity of measurement).
REMARK :That a measurement of a state of a quantum particle (like an electron) disturbs that state (for example the position-momentum state), and results in a fundamental uncertainty, is an interpretation of the quantum measurement experiment. Another interpretation (the Copenhagen interpretation) holds that the particle cannot be considered apart from the measurement device, which means that we cannot speak of a disturbance of the particle by the measurement device. So when a position measurement is done on a quantum particle (with a device that is appropriate for and geared to a position measurement) the momentum of that particle is undefined (instead of being disturbed) [See 't HOOFT, G., 1989, Van Quantum tot Quark, p. 100]. The necessary connection of the object with the measuring device (according to the Copenhagen interpretation) implies some sort of mixing up of object and subject.
That quantum particles are only defined within the context of a macroscopical measuring device could point to their being deficient beings, and as such they perhaps do not fall into the proper domain of Metaphysics, which is about (true) beings [See the Section What is the Investigation about? in the Essay concerned with an Introduction and Overview (of our investigation)].
Of course there are states of affairs which DO depend completely on our thinking and on the way of our thinking, but these are as such recognizable, and distinguishable (be it sometimes with much effort) from things which exist independently of us, because in this case it concerns matters which belong to (the act of) thinking (pertain to thinking insofar as thinking). They clearly originate from ' within '. Often these ' beings of reason ' are completely subjective only at a certain high level, while at a lower level they are one or another in principle objectively describable psycho-physiological activity. Thinking (insofar as thinking) is a phenomenon at a high (complexity)level, that ' floats ' on, and is totally dependent on, physico-chemical activities at a low level.
One can never say that everything is subjective, because this assertion itself pretends to be objective [See The Principle of Motif and Background, in NOTE 3 : subjective knowledge can never be the only form of knowledge, it presupposes the possibility of objective knowledge].
And of course there are certain limits for possible knowledge : Some states of affairs could be so complex (even when they are maximally ' compressed ' by our theories), that they can never become completely known [ Even if we would possess the ' formula of the World', then it could still be impossible to translate this formula into real comprehensive knowledge of the World ]. The amount of information contained in such a complex state of affairs (even stripped of all redundancy) could be so huge that it cannot be comprehended (= grabbed as a whole) in the form of an understood active system (for example the system of the world for that matter), because the brain, as an information-processing device, is limited in its capacity (for storing amounts of information).
But one can never assert (I repeat this again) that objective knowledge is principally impossible, because this assertion itself pretends to be objective knowledge, namely the following :
" The World is such that we cannot know it objectively."
The content of such an assertion that objective knowledge would be impossible, does not square with its intention.
The possibility (and ability) of knowing objectively demands that in the reality that is intended by such knowledge, determination at one or another level must prevail, because an undetermined something is unknowable. Further, genuine knowledge, especially scientific knowledge, implies that we can, on the basis of such knowledge, make predictions that prove to be true. But then in Reality necessity must prevail, and also repeatability.
This repeatability implies in turn that every being, every real entity, must have a Species-Individuum Structure as its ontological composition : A certain nature (Species) can be repeated over individual cases. This ontological structure is equivalent to the (ontological) Form-Matter structure of real material beings (See the Essay on Substance and Accident, first section ).