How Can We Know Truth?

Throughout the centuries there have been many formidable attempts—such as skepticism (David Hume) and agnosticism (Immanuel Kant)—to define the process, parameters, and limits of the human knowing process.

Unfortunately, each has led to conclusions that have effectively separated the knower from the thing known (reality). The ability to know the truth is essential to apprehending knowledge of God (Romans 1:19-21), the gospel (Romans 10:9-10), and comprehending the rich nuggets mined from the words of Scripture, which bring real freedom. This is made clear by Jesus’s words, “You will know the truth, and the truth will set you free” (John 8:32). What is more, if Jesus is “the truth” incarnate (John 14:6) who perfectly corresponds to the Father (John 1:18; 14:9), our knowing the truth has personal and spiritual implications that go far beyond an intellectual exercise to a life-changing experience (John 4:24; 17:3).

We examined and defended the correspondence theory of truth (i.e., statements/truth claims must correspond to reality) against other theories of what truth is. Here we will address how truth is known by reviewing the tests for truth.

Tests for Truth

Language and Logic. There are at least two things that all tests for truth have in common—language and logic.

Pertaining to language, we talk (to ourselves or to others) about the trut that we have confirmed, including how we confirmed it, utilizing categories (subjects and predicates) and copulas (words that link subjects and predicates, such as the word is).[1] With the influence of philosophers such as Ludwig Wittgenstein or A.J. Ayer and philosophies such as logical positivism, deconstructionism, and postmodernism, understanding how truth and language relate, together with how (or whether) each of them relates to reality, is of increasing importance in defending the truth of Christianity.[2]

Regarding logic, we realize that truth claims cannot conflict with eachother.[3] Since the ancient Greeks, Western thinking has recognized that all thinking is governed by fundamental “laws” of logic arising from our grasp of reality. The most basic law is the law of noncontradiction. It says that contradictory statements cannot both be true at the same time and in the same sense or false at the same time and in the same sense.[4]

Thus, if one test seems to yield one conclusion and a different test seems to yield the opposite conclusion, we know that one of the conclusions has to be false— one of the conclusions does not correspond to reality. This tells us that one of the tests is flawed either within it or in how we applied it.

Kinds of Tests. Tests for truth will often differ according to the kind of thing about which a statement is made or a question is asked. Different aspects of reality require different methods of inquiry and tools of analysis. For example, testing a statement about mathematics requires methods of inquiry and tools of analysis appropriate to the mathematical aspects of reality. Testing a statement about history requires methods of inquiry and tools of analysis appropriate to the historical aspects of reality. Testing a statement about a natural science (like chemistry or biology) requires methods of inquiry and tools of analysis appropriate to the physical aspects of reality.

In each case, the key is coming to understand and appreciate these different methods and tools. Sometimes it is easy to see which methods and tools are suitable for a given statement. No one would try to use a calculator to settle a dispute about history, or a microscope to count the moons of Jupiter.

Sometimes, however, knowing which methods and tools should be used on a question can be challenging. There is the danger that one’s assumptions or worldview can interfere with applying the right test. For example, though we know from the testimony of the New Testament that Isaiah wrote the entire book of Isaiah, it has become popular in certain circles of contemporary biblical criticism to say that someone other than Isaiah wrote chapters 40–66 of Isaiah much later.[5] Their argument is that the latter half of the book of Isaiah mentions Cyrus, king of Persia (Isaiah 44:28; 45:1), who lived around two centuries after Isaiah.

What the critics seldom acknowledge is their assumption that Isaiah could not have known the future. While they couch their arguments in the categories of history, literature, and language, the real issue is one of philosophy (does God exist?) and theology (does God reveal the future to His prophets?). They miss the truth of the unity of Isaiah because their assumptions drive them to look in the wrong direction for the proper test for the truth of the matter. Knowing how to test a truth claim requires understanding the kind of statement being made or the kind of question being asked.

Knowing the Truth About Reality. The quest and discovery of truth is really a quest for a discovery of knowledge. Most commonly today in philosophy, one finds the term knowledge defined in three ways. First, knowledge can be a skill. One might say that he knows Italian or that he knows karate. Second, knowledge can be acquaintance. When one says he knows his friend, he is saying that he is acquainted with him. Third, knowledge can be about the truth-value of propositions. Thus, if one knows that 2 + 2 = 4, one knows this as a truth. It is this third definition about which much of contemporary philosophy is concerned. This option, according to the standard view, is what concerns truth.

What is missing from these options is the classical understanding of knowledge one finds from Aristotle through Aquinas and with certain contemporary Aristotelian/Thomistic (or classical) philosophers today.[6]

While this is not the place for an in-depth treatment of epistemology (the philosophy of knowledge), a few observations are in order. First, the classical tradition maintains that all knowledge begins in the senses (known as empiricism).[7] Empiricism says we can know reality by what we see, hear, taste, touch, and smell.[8] It comes in two forms. The more familiar and contemporary version is often associated with the hard sciences, which generally has the consequence of concluding that nothing exists beyond the physical world.[9]

Second, because of the influences of modern philosophy, philosophers have lost the means of accounting for the knower’s connection with the known, or with reality. Such a connection must be at the level of reality (i.e., being) itself. For example, some philosophers argue that we only directly know the ideas in our minds about the external world and not the things themselves in the world.[10] However, if this were the case, there would be no way to stave off skepticism, as the history of philosophy clearly demonstrates.[11]

The only way to account for the fact that the knower truly knows the things in the world is for those things to somehow be in the intellect of the knower. Only then will there be no gap between the knower and the known and, thus, there will be no conditions that would necessarily give rise to skepticism. For example, how can a tree be in the intellect of the one knowing the tree? Since it is by the intellect of the knower that the knowe knows reality, there must be something “intelligible” in the things of the sensible world that allows them to be knowable. This “something” is its Form or (in certain contexts) its essence. The Form is that metaphysical aspect of a thing by virtue of which a thing is the kind of thing it is. For instance, the Form “tree” is what makes all trees to be trees. The Form “human” is what makes all humans to be humans.

The importance of understanding things this way can be seen in the Nuremberg trials, which were held immediately after World War II. The justices of the trials were from the Soviet Union, France, the United Kingdom, and the United States. The Nazi defendants could not be tried on the basis of these countries’ laws because they were not citizens of those countries. Further, the Nazi defendants could not be tried on the basis of the laws of Germany because they hadn’t broken any of Germany’s laws. Hitler had made sure that the constitution and laws of Germany were in place for the final solution to the Jewish question. The basis upon which the Nazi defendants were tried, then, gave rise to an expression that is still in use today: They were said to have committed crimes against humanity.

But, one must ask, exactly what is “humanity”? Is humanity real in any sense of the term real? If one says no, then how could the Nazi defendants have committed crimes against it? If humanity is real, exactly what is its nature? Is humanity male or female, black or white or some other race, tall or short, young or old, sick or well?

In fact, humanity is none of these things. It is what philosophers call a universal. It is that metaphysical aspect of (in this case) a human being that makes one a human. In each human, our humanity (or human nature) is particular, possessing the characteristics of an individual (male or female, young or old, etc.). But through experiencing a sufficient number of human beings, the intellect of a knower is able to abstract that metaphysical aspect (the Form) and know it as a universal. The metaphysical aspect that is able to make the individual human being a human is simultaneously able to exist in the intellect of a knower. Thus, the reality of the individual is in the knower, making the knowledge of things in reality possible. Because there is this metaphysical aspect to physical objects that makes these objects knowable to knowers by way of the intellect, we are able to know the world that God has created.

Remaining Confident in Truth Itself

The ability to know and apprehend truth is crucial to the apologetic endeavor of sharing the gospel and defending the faith. Unfortunately, the innate human potential to know and understand God’s truth has fallen on hard times with the rise of modern philosophy, skepticism, agnosticism, and postmodernism. However, there is no need to abandon confidence in the knowing process or in truth itself, because God has secured access for everyone to knowledge and truth through the things He has made (Romans 1:19-21).

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[1] For example, we observe that all dogs are mammals and that some trees are deciduous. The study of the relationships of such statements is categorical (or Aristotelian) logic. The four forms are: All S is P; No S is P; Some S is P; and Some S is not P. For a helpful introduction to logic, see Norman L. Geisler and Ronald M. Brooks, Come Let Us Reason: An Introduction to Logical Thinking (Grand Rapids, MI: Baker, 1990). For a more in-depth study that deals with the metaphysical grounding for logic, see Peter Kreeft, Socratic Logic: A Logic Text

Using Socratic Method, Platonic Questions, and Aristotelian Principles (South Bend, IN: St. Augustine’s Press, 2008). For a technical exploration of the philosophy of logic according to the classical tradition, see Henry Babcock Veatch, Intentional Logic: A Logic Based on Philosophical Realism (New Haven: Yale University Press, 1952; republished, New Haven, CT: Archon Books, 1970).

[2] It should come as no surprise that how one regards such issues will have a direct bearing on how one reads and interprets the Bible. For an important reading on how language relates to reality, especially as it relates to biblical interpretation, see Thomas Howe, Objectivity in Biblical Interpretation (Altamonte Springs, FL: Advantage Books, 2004).

[3] This is often challenged by postmodernists who resist the constraints of logic and, consequently, resist the classical method of apologetics. See, for example, Robert E. Webber, The Younger Evangelicals: Facing the Challenges of the New World (Grand Rapids, MI: Baker, 2002). Likely influenced (if only indirectly) by Jack Rogers and Donald McKim’s The Authority and Interpretation of the Bible: An Historical Approach (New York: Harper & Row, 1979), Webber’s defense of postmodernism exhibits a very common misunderstanding of the history of ideas, particularly regarding the notion of truth and logic, and their bearing on proclaiming and defending the message of Christianity.

[4] We can see this law in Genesis 3:1-5, where God said that Adam and Eve would die the day they ate of the tree of the knowledge of good and evil. Satan contradicted God and said they would not die. These statements cannot both be true at the same time and in the same sense.

[5] For a quick summary of the arguments for Isaiah being the author, see Normal Geisler and Thomas Howe, When Critics Ask: A Popular Handbook of Bible Difficulties (Wheaton, IL: Victor Books, 1992), 265-267. For a more in-depth analysis and defense of the single authorship of Isaiah, see Oswald T. Allis, The Unity of Isaiah: A Study in Prophecy (Phillipsburg, NJ: Presbyterian & Reformed, 1980).

[6] For a helpful summary of the philosophy of Aquinas, see Edward Feser, Aquinas: A Beginner’s Guide (Oxford, UK: Oneword, 2010). Feser has also written a more in-depth treatment of Aquinas’s philosophy in Scholastic Metaphysics: A Contemporary Introduction (Piscataway, NJ: Transaction Publishers, 2014). For a good treatment of Aquinas’s philosophy in the context of defending it against other interpretations of Aquinas in contemporary

philosophy, see John Knasas, Being and Some 20th Century Thomists (New York: Fordham University Press, 2003). For a treatment of Aristotle (the philosopher who influenced Aquinas) by contemporary philosophers, see

Edward Feser, ed., Aristotle on Method and Metaphysics (London, UK: Palgrave Macmillan, 2013).

[7] Aquinas wrote, “Sensible things [are that] from which human reason takes the origin of its knowledge.” See Summa contra Gentiles, I, 9, §2., trans. Anton C. Pegis (Notre Dame, IN: University of Notre Dame Press, 1975), I, 77. Elsewhere he says “Our knowledge, taking its start from things, proceeds in this order. First, it begins in sense; second, it is completed in the intellect.” See Truth, I, 11, trans. Mulligan, 48, in Truth (3 vols.), vol. 1 trans. Robert W. Mulligan (Chicago, IL: Henry Regnery, 1952); vol. 2 trans. James V. McGlynn (Chicago, IL: Henry Regnery, 1953); vol. 3 trans. Robert W. Schmidt (Chicago, IL: Henry Regnery, 1954). The three volumes were reprinted as Truth (Indianapolis, IN: Hackett, 1994). Other comments by Aquinas in this regard include: “Our senses give rise to memories, and from these we obtain experiential knowledge of things, which in turn is the means through which we come to an understanding of the universal principles of sciences and art.” See Summa contra Gentiles, II, 83, §26. Trans. James F. Anderson, II, 279; “Our knowledge of principles themselves is derived from sensible things.” See Summa contra Gentiles, II, 83, §32., trans. James F. Anderson, II, 282.

[8] The Bible demonstrates that empiricism can give us knowledge even about God. Repeatedly, both in the Old Testament and the New Testament, God and His prophets and apostles appealed to what we experience with our senses to demonstrate His truths. For example, see Deuteronomy 29:2-3; Luke 1:1-4; Acts 10:37-41; and 1 John 1:1-3. Romans 1:20 tells us that the invisible attributes of God are clearly seen, being understood by the things that are made. Jesus appeared to His disciples and showed Himself physically to their senses (to Mary and other women—Matthew 28:1-10; to the two disciples on the way to Emmaus—Luke 24:13-35; to the ten disciples—Luke 24:36-49; to

[9] In its earliest manifestation in contemporary thinking, this philosophy was known as logical positivism. It was exemplified in the thinking of A.J. Ayer in his work Language, Truth, and Logic (New York: Dover, 1952). Ayer was famous for formulating (and then soon thereafter repudiating) the verificationist principle, which said that only those statements that are true by definition or empirically verifiable are meaningful. It was quickly recognized that the verificationist principle did not meet its own standard of being a meaningful statement. For a critique of other aspects of Ayer’s philosophy, see Richard G. Howe, “On the Function of Philosophy,” Christian Apologetics Journal 7, no. 2 (Fall 2008): 57-82. Today, such erroneous thinking (known disparagingly by its detractors as scientism) is not uncommon among scientists. Regarding the question of God’s existence, Richard Dawkins asserts, “The presence or absence of a creative super-intelligence is unequivocally a scientific question, even if it is not in practice—or not yet—a decided one.” See Richard Dawkins, The God Delusion (Boston, MA: Houghton Mifflin, 2006), 58-59. Marcia McNutt, president of the National Academy of Sciences, said, “Science is not a body of facts. Science is a method for deciding whether what we choose to believe has a basis in the laws of nature or not.” See in Joel Achenbach, “The Age of Disbelief,” National Geographic (March 2015): 40.

[10] Such is the philosophy of John Locke (1623–1704), who said, “Since the Mind, in all its Thought and Reasonings, hath no other immediate Object but its own Ideas, which it alone does or can contemplate, it is evident, that our Knowledge is only conversant about them…’Tis evident, the Mind knows not Things immediately, but only by the intervention of the Ideas it has of them. Our Knowledge therefore is real, only so far as there is a conformity between our Ideas and the reality of Things.” See John Locke, An Essay Concerning Human Understanding, IV, I, 1, §1 and IV, I, 4, §3, ed. Peter H. Nidditch (Oxford, UK: Clarendon Press, 1975), 525, 563.

[11] Étienne Gilson, The Unity of Philosophical Experience (San Francisco, CA: Ignatius Press, 1999).