In the area of epistemology, we ask what can be known, and the means by which we can know, and how we can be certain of what we know. Both subjectivity and objectivity work together in our epistemological inquiries; this seems startling to some, obvious to others, and nonsense to the third group. It's startling, because it seems that on the surface, knowledge--or truth claims--cannot be both subjective and objective; they are one or the other. The second group, subsumed under the auspices of a postmodern, post-structuralist paradigm, give a passive nod, noting with laissez faire that man is the center, and that truth-claims are ultimately relative to the individual, or at least to the group to which he belongs. The third group demands complete objectivity and rears in horror at the idea of any subjectivity in the area of knowledge, for, how can man have a starting point or an Archimedean pou sto (a lever with which to move the world) if knowledge is nothing except objective in nature?
Realizing that Francis Schaeffer is passe for students of epistemology with the plethora of research done in this area, Alvin Plantinga leading the charge in his Aquinas/Calvin model, we can still learn a thing or two from the 40 year-old book, He is There and He is Not Silent. Schaeffer gets the title from Wittgenstein, who spoke of the mystical silence at the end of the linguistic road in man's search for knowledge (believing that all language boils down to "games" between different groups or individuals, thus reducing language to pure subjectivity and ultimate meaninglessness [the latter phrase being a contradiction]).
Now, Schaeffer asks us to consider two different presuppositions--or starting points--when making our epistemological inquiry: 1) the uniformity of natural causes in a closed system and 2) the uniformity of natural causes in a limited system, open to reordering by God and by man. The latter is the Christian view, and Schaeffer argues that 1) does not provide an actual uniformity of all particulars, but 2) does (see chapters 3&4 of the book for the argument).
In the basic scheme of the area of knowledge we speak of the subject, the object and the means by which the object is known. We might think of a simple, grammatical form of a sentence and its primary parts: subject, verb, object. These three parts make up one, complete sentence, and yet the parts are distinct and separate. Still, they are dependent upon one another in order to make a sentence (leave aside for the moment that a sentence can be a sentence without an object [a direct object] in the case of a predicate nominative ['I am"]). So we have the knower and the known, and we have the means by which the known is known. The knower as the subject, attempts to know the object, the known. When the subject "knows" the object, he has "knowledge" of it.
While understanding all the problems, issues, and technicalities important in the area of justifying knowledge claims is an encyclopedic task, it's worthy to note that the concept of subjectivity should be a welcome term in the area of Christian knowledge, especially as the Christian desires to assure the world that knowledge can indeed be known with certainty; we are not left to our devices in a quagmire of relativity. So, let's not confuse subjectivity with relativity.
By way of example, Schaeffer tells his classic story of asking his wife for a pot of tea. Now, in his wife's understanding and background of tea, there is the experience of China, where one packs rice into the mouth and drinks the tea with the rice tucked away so that the tea doesn't affect the consumption of the rice: the tea goes around the rice. In Mr. Schaeffer's experience of tea, he goes to Germantown in Philadelphia to make tea with a caddy. These two experiences of "tea" are vastly different, and yet Schaeffer asks, that when he asks his wife for a pot of tea, though each of them have entirely different paradigms for understanding what "tea" is, "Do I not get a pot of tea?" Schaeffer's point is this: he advises us to avoid the two extremes of first, over-literalizing language to the point where each has an absolutist, and hence, self-particular, understanding of his words, and second, throwing up our hands and giving up on the idea that language carries any meaning with it that is not entirely lost in the mystery of the universal search for meaning. It's interesting to note that on either case, epistemological searches for certainty by use of language end up in complete subjectivity and relativism. One the first scenario, the absolutist has a personal, restricted understanding of what "tea" is, and it reduces to that one, particular experience of tea. She can no longer communicate to others what "tea" really is, because her experience is hers and hers alone, and no one else's. On the second extreme, language is subsumed under the realm of "complete mystery" because it fails to bring a unity to one's experience in life.
This is the epistemological problem Schaeffer talks about in his book: that there is no unifying factor in the area of knowing particulars. In chapter 4 of He is There and He is Not Silent, Schaeffer presents the Christian view of epistemology that God, as the unifying factor brings all the particulars together under his exhaustive knowledge of things. Humans do not have exhaustive knowledge of things, but they know things truly, because the One who knows exhaustively gives them meaning, stands as an ultimate referent, and holds them all together. The Christian starting point of the uniformity of natural causes in an open system provides the unity amidst the particulars in the area of knowledge, with the Triune God as the foundation and model of that starting point. .
So, in the area of knowledge, on the Christian view, knowledge is not only "objective," but "subjective" as well. That is, there is a Knower, God, and God is the Subject who knows us, the objects. In this respect, knowledge is subjective. That is not to be confused with the idea that knowledge is relative, and subject to the finite, human inquiry after things. If that were all we had--the uniformity of natural causes in a closed system--then yes: knowledge is completely subjective and relative (though this, too, is a contradiction). It becomes, then, a matter of perspective, when we speak of knowledge as subjective or objective: if we mean knowledge is subjective as an end, then we are starting from the wrong place (a closed system) and ending up with the black hole of mysticism and relativism. If we mean knowledge is subjective as a starting point, then we are in the right place, as we consider a world created by God to be known, who has made us in his image as knowers. As Schaeffer notes: it should not surprise us that on the Christian view of God and things, that humans could know truly, though not exhaustively. And humans know Subjective knowledge in an objective way, because they know the objects (the created order, themselves, and the Creator) because of the Subject, the infinite-personal God.