How do Christians know that their belief in the Trinity is rational, justified, and true? For centuries, theologians and apologists have wrestled with this question, seeking an epistemological framework that upholds both revelation and intellectual integrity. This article presents a dual epistemological approach: combining sensus divinitatis—an innate sense of the divine—with the power of reason. Drawing from Reformed epistemology and classical rationalism, I argue that belief in the Trinity can be both properly basic and philosophically coherent.
The Importance of Epistemology in Christian Theology
Epistemology, the study of knowledge and justified belief, is foundational to Christian philosophy. As Norman Geisler notes, it explores how we know, what counts as justified belief, and how to respond to skepticism.¹ J.P. Moreland identifies four branches: conceptual clarity, the problem of skepticism, the scope of justified belief, and criteria for justification.² Every theological assertion—especially complex doctrines like the Trinity—requires epistemological grounding.
James K. Dew defines knowledge as a belief that is true and justified,³ and highlights epistemology’s role in distinguishing truth from opinion. In Christian theology, this distinction is crucial when confronting postmodern relativism and defending doctrinal orthodoxy.
Reformed Epistemology and the Role of Sensus Divinitatis
Reformed epistemology, popularized by Alvin Plantinga and Nicholas Wolterstorff, challenges classical foundationalism and evidentialism. It posits that belief in God can be “properly basic”—rationally held without propositional evidence.⁴
At the heart of this approach is sensus divinitatis, a term used by Calvin and Aquinas to describe the innate human capacity to perceive God.⁵ According to Plantinga, this faculty, when functioning properly, produces warranted true beliefs about God.⁶ Scripture affirms this in Romans 1:19–20 and Romans 2:14–15, where Paul describes divine knowledge as imprinted on the human heart.
Plantinga argues that such beliefs, arising from properly functioning cognitive faculties in suitable epistemic environments, can be considered knowledge.⁷ This offers believers a non-inferential epistemic grounding for the doctrine of the Trinity—not based on argument, but on divine revelation apprehended through spiritual intuition.
Rationalism: Reasoning Toward Divine Truth
While sensus divinitatis initiates belief, reason plays a complementary role in refining, defending, and articulating it. Rationalism prioritizes logic and coherence in the pursuit of theological truth. Acts 17:11 praises the Bereans for examining Scripture with intellectual rigor—a model of reasoned faith.
Moreland identifies three senses of rationality: cognitive capacity, deliverances of reason, and warranted justification.⁸ He affirms that Aquinas blends rationalism and revelation, suggesting that reason is needed before, during, and after faith is acquired.⁹ Geisler and Augustine agree that reason enables immediate apprehension of divine truths deposited in the mind by God.¹⁰
Jonathan Edwards outlines eight functions of reason in relation to revelation—including verifying its authenticity, demonstrating its dependability, and defending its mysteries.¹¹ This affirms reason’s indispensable role in theological formulation and apologetic engagement.
Applying Sensus Divinitatis and Reason to the Doctrine of the Trinity
The Trinity, while not overtly named in Scripture, emerges from biblical revelation. Though some see it as a philosophical construct, theologians like Henry Thiessen, Paul Enns, and Millard Erickson affirm its foundation in divine revelation.¹² Thiessen asserts that “reason may show us the unity of God,” while Enns acknowledges the doctrine’s complexity and scriptural grounding.¹³
Is belief in the Trinity properly basic? While the word “Trinity” is absent, the foundational belief in one God—and in the divinity of Jesus and the Holy Spirit—is grounded in sensus divinitatis. Reason then builds upon this foundation to articulate coherence and avoid heretical missteps like tritheism or modalism.¹⁴
Through logical reasoning, Christians interpret passages like Matthew 28:19 and John 1:1 to affirm both the unity and plurality of the Godhead. The analogies offered by Augustine and Thiessen—though imperfect—help frame the doctrine within human cognition, guided by reason.
Justification, Rationality, and Warrant ️
According to Plantinga, a belief is justified if, after careful reflection, it remains compelling.¹⁵ The freedom Christians have to examine competing worldviews—while consistently returning to Trinitarian belief—underscores its epistemic strength.
A belief is rational if produced by properly functioning faculties aimed at truth, not wishful thinking.¹⁶ The doctrine of the Trinity, far from irrational, is supported by rigorous theological analysis and historical reflection.
Finally, warrant requires a high probability that a belief, produced by suitable cognitive faculties in the right environment, is true.¹⁷ The theological tradition, scriptural testimony, and enduring orthodoxy of the Trinity all suggest a warranted belief.
Conclusion: Faith Seeking Understanding ️
By integrating sensus divinitatis and reason, Christians can affirm the Trinity as a justified, rational, and warranted belief. While revelation initiates faith, reason enriches and defends it. This epistemological symbiosis offers a compelling framework for engaging skeptics, nurturing believers, and safeguarding theological truth.
As Plantinga affirms, our cognitive faculties are designed for truth—and when they function rightly, they lead us to knowledge of God. In the doctrine of the Trinity, that knowledge becomes both profound and transformative.
References
- Norman L. Geisler, The Big Book of Christian Apologetics (Grand Rapids, MI: Baker Books, 2012), 213.
- J.P. Moreland, Philosophical Foundations for a Christian Worldview, 2nd ed. (Downers Grove, IL: IVP Academic, 2017), 71–72.
- James K. Dew and Mark W. Foreman, How Do We Know? 2nd ed. (Downers Grove, IL: IVP Academic, 2020), 25.
- Alvin Plantinga and Nicholas Wolterstorff, Faith and Rationality (Notre Dame, IN: University of Notre Dame Press, 1983), 2.
- Alvin Plantinga, Knowledge and Christian Belief (Grand Rapids, MI: Eerdmans, 2015), 31.
- Ibid., 36–37.
- Ibid., 46.
- Moreland, Philosophical Foundations, 85.
- Ibid., 85.
- Geisler, Christian Apologetics, 105, 259.
- Ibid., 205.
- Henry C. Thiessen, Lectures in Systematic Theology (Grand Rapids, MI: Eerdmans, 2006), 89; Paul Enns, The Moody Handbook of Theology, 25th ed. (Chicago: Moody Publishers, 2014), 205; Millard J. Erickson, Christian Theology, 3rd ed. (Grand Rapids: Baker Books, 2013), 345.
- Thiessen, Systematic Theology, 90; Enns, Theology, 205.
- Erickson, Christian Theology, 366.
- Plantinga, Knowledge and Christian Belief, 46.
- Ibid., 46.
- Ibid., 38.
Bibliography
Dew, James K., and Mark W. Foreman. How Do We Know? 2nd ed. Downers Grove, IL: IVP Academic, 2020.
Enns, Paul P. The Moody Handbook of Theology. 25th ed. Chicago: Moody Publishers, 2014.
Erickson, Millard J. Christian Theology. 3rd ed. Grand Rapids: Baker Books, 2013.
Geisler, Norman L. The Big Book of Christian Apologetics. Grand Rapids, MI: Baker Books, 2012. Moreland, J.P. Philosophical Foundations for a Christian Worldview. 2nd ed. Downers Grove, IL: IVP Academic, 2017.
Plantinga, Alvin, and Nicholas Wolterstorff. Faith and Rationality. Notre Dame, IN: University of Notre Dame Press, 1983.
Plantinga, Alvin. Knowledge and Christian Belief. Grand Rapids, MI: Eerdmans, 2015.
Thiessen, Henry C. Lectures in Systematic Theology. Grand Rapids, MI: Eerdmans, 2006.
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