John Locke on Reason and Faith

The 17th Century Background of American Unitarianism

© by Dr. Jan Garrett

Slightly modified: March 8, 2007


The unitarian movement which eventually became the American Unitarian Association and merged in mid-twentieth century with Universalism to become the Unitarian-Universalist Association is rooted in the liberal Protestantism of congregational churches in eighteenth century New England. But if we trace the roots back further we come to the liberal wing of the Puritan movement in seventeenth century New England and England.

Religious Liberalism

"Liberalism" is a word with many meanings. It is not often these days that we hear it associated in a positive way with religion. So it may be useful to distinguish religious liberalism from two other, more familiar kinds of liberalism. One kind of liberalism is the free-market, small government philosophy of Adam Smith, whose most recent incarnation is the "neoliberal" ideology of privatization and open markets. A second kind of liberalism is social-services or welfare state liberalism, associated in the popular mind with Franklin Delano Roosevelt and the New Deal, which favors substantial government action to help the disadvantaged and often appears to be the opposite of free-market liberalism, at least in its extreme form.

Religious liberalism, which is at least as old as free-market liberalism, refers to support for the principles of religious freedom--tolerance, separation of church and state, and the right of individuals to use their rational faculties in the interpretation of Scripture. Religious liberalism tends to reject the idea of heresy, that is, the idea that you should be expelled from your church, your property, or your job, or burnt at the stake, for holding views contrary to those of religious authorities.

Early Modern Unitarianism

Liberal British Protestantism developed partly out of and in reaction to Calvinism. These liberals tended to reject Calvin's harsher teachings, such as the inherited depravity of human nature and predestination. Moreover, they tended to reject the Trinity, i.e., the view that Jesus was one of three eternal persons making up the one substance of God. Thus liberal religion tended towards "unitarianism." British religious liberals were also influenced by a European unitarian movement known as Socinianism (named after Faustus Socinus, an Italian Protestant reformer).(1) In the sixteenth century the Socinians developed a large following in Poland.

John Locke

My main focus in this talk is the religious ideas of John Locke (1632-1704). Locke is well-known as the founder of the philosophy which John Stuart Mill later named empiricism. Locke is also well-known as a political thinker whose views on rights to life, liberty and property are influential today. What is not so well known is that Locke's Essay Concerning Human Understanding, first published in 1689, has a lot to say concerning the relation between reason and faith.

Locke a Unitarian

It is even less well known that in his later years, Locke was a unitarian. Professor Nicholas Woltsterstorff, who is not a Unitarian, defends this claim in a recent publication. So did Herbert McLachlan, principal of the Manchester (England) Unitarian College, who gave the conclusion of his book The Religious Opinions of Milton, Locke and Newton (1941) the title "Milton, Locke, Newton and Other Unitarians." (2) McLachlan writes, "The evidence, direct and indirect, is conclusive. John Locke was a Unitarian; cautious, conservative and scriptural; in all three respects resembling most Unitarians [before the nineteenth century]" (107).(3)

Formally, Locke belonged to the dominant Anglican Church, but within the Anglican Church, he was an advocate of the broad church, or latitudinarianism. The broad church held that all that was required to belong to the Church was that you believed what Jesus taught about God and human salvation.

Influence on American Unitarianism

Locke's writings were widely read in New England during the eighteenth century and thus exercised considerable influence on the liberal Protestants who eventually gave rise to American Unitarianism. This is attested to by George Willis Cooke in his respected History of American Unitarianism (Cooke 1902, 12-13). Cooke writes that "Unitarianism had its origin . . . in the teachings of men who were counted orthodox in England but who favored submitting all theological problems to the test of reason. . . . It was an effort to make religion practical, to give it a basis in reality, and to establish it as acceptable to the sound judgment and common sense of all men" (14).(4)

Advocate of Tolerance

Locke is a public philosopher, concerned with issues regarding moral and religious belief. He is well aware there are several versions of Christianity, each of which claims to be true religion. He knows that this variety is not going to disappear. Earlier Christians often tried to resolve disputes by appeals to tradition and to the traditional authorities centered in the Catholic Church. But such appeals were no longer persuasive for most Englishmen.

Locke offers his philosophy as a way to use reason, a shared human capacity, to decide how much credibility a person should give to the claims people make. Though much of his Essay concerning Human Understanding is about the extent and limits of our knowledge of nature, Locke was more concerned with religious and moral matters. (Passages cited from Locke in what follows are from the 1975 Oxford University Press edition of the Essay, unless otherwise indicated.)

He is also concerned to promote religious tolerance. Among his writings is his Letter on Tolerance. Locke believes that too much blood has been shed over matters of faith. He makes a distinction between what can be known and what must be taken on faith. In his view neither knowledge nor faith demand the use of force against persons who differ intellectually or religiously. Where reason can supply an answer to a question, there are rational methods to resolve a dispute, thus no need to quarrel. Where faith alone is the way to answer it, no methods of reason can be persuasive. Hence there is no justification for using force.

Essay concerning Human Understanding

Locke's Essay concerning Human Understanding appears at first to be about the basis and extent of human knowledge. Its first book contains a famous attack on the view that humans are born with some ideas already in their minds, the doctrine of innate ideas. This attack is meant to support Locke's empiricist view that all our ideas derive from experience.

Experience is either external or internal. External experience provides us with ideas that come in through the five senses (sight, smell, hearing, etc.). Internal experience provides us with ideas that form when we reflect on our own mental operations, such as doubting, reasoning, and sense-perception itself. In Book II Locke tells how our ideas arise through sensation or reflection, or combinations of the two. The unjustly underrated third book contains a study of the part played by language in communication and failures to communicate.

But Book IV is what interests us here. A look at its contents tells us that Locke is going to treat both knowledge and belief and distinguish between them. He is going to insist that our knowledge in fact is quite limited, more so than many think, but that some of our beliefs have a reasonable foundation and may be accepted. Faith, it turns out, is a particular kind of belief, sometimes worth accepting and sometimes not.


Knowledge, according to Locke, is an activity of the human mind. Knowing involves ideas and, through ideas, relates to things (Essay iv 1.1).

Locke regards knowledge (iv 1.2) as grasping the agreement or disagreement of our ideas. Knowledge sometimes concerns sameness or difference (red is a color, triangle is not square); sometimes relation (two is greater than three); sometimes necessary connection (in the thing called gold, yellowness accompanies malleability); and sometimes existence (each of us can know, Locke thinks, that he or she exists and that God exists).

Locke distinguishes three degrees of knowledge (iv 2): Intuitive knowledge directly perceives the agreement or disagreement of two ideas, without the help of any other idea. "Intuition" in Locke's vocabulary is not a hunch but a clear act of mental insight. We can know by intuition that red is not blue, that the idea of red and the idea of blue disagree. Moreover, I know by intuition that I exist (iv 3.21).

Intuitive knowledge is thus the least doubtful of all. The second degree of knowledge, called demonstrative, is almost as certain as intuitive. Suppose you use the strictest kind of reasoning, the kind used in mathematics. Suppose that you start from ideas already known by clear mental insight. Then your conclusions will be demonstrative knowledge. Locke believes that he can demonstrate and therefore know the existence of God, i.e., an eternal being more powerful and more knowing than any other (iv 3.21).

The first two "degrees" of knowledge deal with truths which cannot conceivably be false. Some of them seem quite trivial, but others, such as Locke's alleged demonstration that God exists, are obviously not.

The third kind of knowledge is "a perception of the particular existence of finite beings outside us" (iv 2.14, p. 537), for example, that there are colored objects in front of us, hard objects underneath us. Some philosophers claim that the existence of material things outside us is always doubtful, because our senses are untrustworthy. Locke says (p. 537):

Whether there be any thing more than barely that [concrete] Idea in our Minds . . . is that whereof some men think there may be a question made. . . . But yet here . . . we are provided with an evidence, that puts us past doubting: For I ask anyone, whether he be not invincibly conscious to himself of a different perception when he looks on the sun by day, and thinks on it by night.
This knowledge of external things, which Locke calls sensitive knowledge, is less certain than the other kinds.

Limits of Knowledge

Moreover, it is very limited. Our sensitive knowledge does not extend beyond the existence of things immediately given to the senses. Material things probably continue to exist when we do not directly perceive them, but this is not certain.

In any case, says Locke (iv 3.1-3.6), reality is broader than our ideas and our ideas are broader than our knowledge . In other words, there are things of which we have no ideas and many of our ideas are uncertain or false.

As we have seen, Locke holds that our knowledge of the external world is very limited (6.15). We cannot know with certainty, he says, that all men sleep by intervals or that no man can be nourished by wood or stone (p. 590). Why? Because we do not see the necessary link between, say, being human and sleeping by intervals--we could do this only if we could somehow penetrate to the real essence of humanity. But he says we cannot do this.

The scope of true human knowledge, of certainty, is "very short and scanty," says Locke. With regard to most things we care about, God "has afforded us only the twilight . . . of Probability." This limitation, he says, was given us "to check our over-confidence and presumption," to make us "by every day's experience ... sensible of our short-sightedness and liableness to error" (iv 14.1).


But all is not lost--we have also been given the faculty of judgment. Judgment is the capacity the mind uses when it "takes its ideas . . . to be true, or false, without perceiving a demonstrative evidence in the proofs," in short, when we are lacking the means of the strictest logic. Judgment is the act of putting ideas together in the mind, or separating them in the mind, when their agreement or disagreement is not perceived to be certain but only presumed to be so.

When the mind unites, or separates ideas, as things really are, then this is right judgment. Thus, if my mind unites the idea of Nixon and the idea of crook, without perceiving the link as certain, but Nixon really was a crook, then this is not knowledge but right judgment (iv 14.4).

Degrees of Assent

To assent to an idea is to receive it as true. Now, there are degrees of assent, just as there are degrees of probability that our judgments are right. Faith will turn out to be a special type of assent (p. 655.14).

Probability (iv 15.3) is likeliness to be true. It is the contrary of certainty. (Locke would not have understood the phrase "probability of 100 %.") Probability relates to statements about which "we have no certainty but only some inducements" to regard them as true (iv 15.4). Such inducements may include:

1) the agreement of something with what we do know, with our observation and experience; and

2) the testimony of others.

Here we should proceed carefully and consider such factors as:
(a) number of witnesses;
(b) their reliability ("integrity");
(c) their skills;
(d) the intent ("design") of the speaker or writer;
and (f) contrary testimonies.

Locke emphatically rejects uncritical reliance on the opinions of others as "no true ground of probability" (iv 15.6).

He distinguishes several degrees of probability. The highest degree he calls assurance. Given his examples, assurance seems to concern general judgements about how material things interact: for example, fire warms a person, iron sinks in water. It is proper to be assured when the truth of a claim for which there are good witnesses is supported by the agreement of all people, in all ages, so far as it can be discovered.

A second highest degree of probability, confidence, attaches to judgments concerning a particular when it is witnessed by others and is consistent with general judgments about what is usually true. These general judgments themselves can be supported by one's personal experience with the ways in which people or things behave and by the agreement of all other persons. Locke gives an example involving an historical judgment about the Roman emperor Tiberius.

Other types of probability do not depend upon the testimony of others and one's own experience. Some concern things not falling in the reach of our senses-- either above us (spirits), below us (microscopic beings too small to see), or too far away from us (life and intelligence on other planets). Here, Locke thinks that, if we are cautious enough in reasoning by analogy, we may obtain correct judgments.

Faith and Reason

Faith is a special case (iv 16.14). At one point Locke defines it in terms of revelation from God.(5) Faith is "a settled and sure principle of assent and assurance, and leaves no manner of room for doubt or hesitation." But there is an irony in this apparently quite positive definition of faith. You can have such faith only if your assent is a response to testimony received from God himself, i.e., through revelation. God himself does not lie. For, in Locke's view, it is a self-evident truth that God, if He exists, is good (p. 667.25-26). And Locke believes that we can prove that God does exist (see iv 10).

The big question for Locke is this: how do we know that a testimony, which claims to be from God, is in fact from God? "Our assent can rationally be no higher than the evidence of its being a revelation, and that this is the meaning of the expressions it is delivered in" (iv 16.14). In other words, we have a duty to check the credentials of someone who or something which claims to bring a revelation from God and to ask how sure we are that we have the right interpretation of it.

Locke next defines reason and distinguishes it from faith: Reason, he says, is

the discovery of the certainty or probability of such propositions or truths which the mind arrives at by deductions [inferences] made from such ideas which it has got by use of its natural faculties, viz. by sensation and reflection (iv 18.2).

Thus reason is concerned with the three degrees of knowledge discussed earlier and the most probable kinds of judgments. In contrast to reason, faith is said to be assent to a proposition not on the basis of reason but on the authority of the proposer as coming from God in some extraordinary way. Such extraordinary communication is called revelation.

Revelation is of two types. Original revelation is "that first impression, which is made immediately by God, on the mind of any man." Traditional revelation is "those impressions delivered over to others in words and the ordinary ways of conveying our conceptions one to another" (iv 18.3). A prophet might hear God directly by original revelation but when he writes it down or tells another person, that's derivative, or traditional, revelation.

Derivative revelation is handicapped in a number of ways: The farther removed from its original source, the greater the danger that it has been corrupted in transmission. The more unfamiliar the language in which it is originally expressed, the greater the likelihood that it will be misinterpreted. Moreover, traditional revelation cannot communicate to us any simple idea which we have not already received through the senses. (Thus, if I have never experienced the color red or the taste salty, this idea cannot be revealed to me by traditional revelation; though it could by original revelation.) Nor can traditional revelation give us any new complex idea whose understanding relies upon simple ideas for which we lack experience (iv 18.3).

Now, some truths might be conveyed by revelation that could also be discovered by reason. If God so chose, He could directly reveal mathematical truths to us and these could then be conveyed from person to person by means of language. Yet we can never be as certain about truths received in this way as we could if we reasoned them out ourselves and had strict deductive proof for them. When we have such proof, we have no need for revelation.

Reason gives us more certainty than faith, Locke holds, and it should be given more weight than revelation when the self-evident claims of reason clash with statements that supposedly come from revelation. Locke thinks it is a psychological fact that "faith can never convince us of anything that contradicts our knowledge" (p. 692).

What things may be accepted on faith?

(i) Things about which reason is incompetent to decide ("things above reason") such as whether the dead shall be resurrected (iv 18.7);

(ii) Some things contrary to the probable conjectures of reason (iv 18.8).


Locke does not give an example at this point but probably he has in mind what he discusses in an earlier chapter. Supernatural events, or miracles, may be used by God to get our attention when he is trying to reveal something of utmost importance. Therefore we sometimes ought to believe testimony about a supernatural event if it comes from a reliable witness. The importance of the revelation and the extraordinary nature of the miracle seem to confirm one another.(6)

Nicholas Wolterstorff writes on this topic, that Locke "assumes that if we do as we ought and subject the testimony of the gospel writers to the same evidential tests to which we subject any other testimony . . . we will arrive at the conclusion that their testimony is reliable. In particular, Locke never doubted that the deeds of Jesus to which the gospel writers testify and which they interpreted as miracles, were in fact miracles; and further, that these miracles authenticated Jesus' prophetic status" (Chappell, 195-96).(7)

Locke believes that morality could be a strictly demonstrative science; that is, we might some day reach ethical conclusions as free from doubt as the conclusions of mathematics. However, he is aware that acquiring this knowledge is more difficult than acquiring mathematical knowledge. In the absence of a true moral science, we are blessed to have moral teachings revealed to us by God through Jesus. God gave Jesus the power to perform miracles because He did not wish these moral teachings to be overlooked.

Properly Regulated Faith Not Opposed to Reason

In admitting divine revelation, Locke does not abandon reason. It has a job to do, first, in judging whether what claims to be a divine revelation is in fact one and, second, what the words or signs through which the revelation is delivered actually mean.

Locke wrote (iv 17.24):

Faith is nothing but a firm Assent of the Mind: which if it be regulated, as is our Duty, cannot be afforded to anything but upon good Reason; and so cannot be opposite to it. He that believes, without having any Reason for believing, may be in love with his own Fancies; but neither seeks Truth as he ought, nor pays the Obedience due his Maker, who would have him use those discerning Faculties he has given him, to keep him out of mistake and errour.


1. R. H. Kane (1995, p. 748) has the following to say about Socinianism. It "accepts Christ's message as the definitive revelation of God, but regards Christ as human, not divine; rejects the natural immortality of the soul, but argues for the selective resurrection of the faithful; rejects the doctrine of the Trinity; emphasizes human free will against predestination; defends pacifism and the separation of church and state; and argues that reason--not creeds, dogmatic tradition or church authority--must be the final interpreter of Scripture. Its view of God is temporalist: God's eternity is existence at all times, not timelessness, and God knows future free actions only when they occur."

2. Wolterstorff (in Chappell 1995, 185) writes, "It is indeed fairly clear that in his theological views Locke was a Socinian (unitarian) for the last decade and a half of his life." McLachlan presents evidence that Locke, while a Unitarian and on friendly terms with a number of unitarians who were Socinians, was not a Socinian himself. Rather than seek religious ideas in the texts of the Socinians Locke preferred to look in Scripture. Locke wrote "I know not but it may be true, that the Antitrinitarians and Racovians (Socinians) understand these places as I do, but tis more than I know, that they do so. I took not my sense of those texts from those writers, but from the Scripture itself ..." (quoted in McLachlan 1941, 99). It is important to note that there were at least three ways of being a Unitarian in Locke's time and Socinianism was only one of them. Clapp 1967, 502, denies that Locke was a Socinian or a deist, but implies, without textual references, that Locke accepted the divinity of Christ. McLachlan, 90ff., shows why arguments for the denial of Locke's Unitarianism are inconclusive.

3. The cautious and scriptural character of Locke's Christianity is clearly displayed in The Reasonableness of Christianity, first published anonymously in 1695 (Locke, 1965). But on Locke's reading, in addition to faith and grace, works are important. Applying his own reason to the interpretation of the Bible, Locke found it teaching not only that Jesus was the Messiah or Son of God and that faith in this claim was required for salvation, but also the following:

. . . our Savior not only confirmed the moral law and, clearing it from the corrupt glosses of the scribes and Pharisees, showed the strictness as well as obligation of its injunctions; but moreover, upon occasion, requires the obedience of his disciples to several of the commands he afresh lays upon them, with the enforcement and punishments in another world, according to their obedience or disobedience. There is not, I think any of the duties of morality which he has not, somewhere or other, by himself and his apostles, inculcated over and over again to his followers in express terms. And is it for nothing that he is so instant with them to bring forth fruit? Does he, their King, command, and is it an indifferent thing? Or will their happiness or misery not at all depend on it, whether they obey or not? They were required to believe him to be the Messiah, which faith is of grace promised to be reckoned to them for the completing of their righteousness, wherein it was defective; but righteousness, or obedience to the law of God, was their great business, which if they could have attained by their own performances, there would have been no need for this gracious allowance in reward of their faith. . . . Their obligations had never ceased, nor a wilful neglect of them was ever dispensed with. But their past transgressions were pardoned to those who received Jesus, the promised Messiah, for their king; and their future slips covered, if, renouncing their former iniquities, they entered into his kingdom and continued his subjects with a steady resolution and endeavor to obey his laws. This righteousness, therefore, a complete obedience and freedom from sin, are still sincerely to be endeavored after. And it is nowhere promised that those who persist in a wilful disobedience to his laws, shall be received into the eternal bliss of his kingdom, how much soever they believe in him. (148-149)

4. Cooke (1902) also writes: ". . . the Son of God presented in the New Testament is less exalted than the Father. This conception of Christ is technically called Arianism, from [Arius,] the Alexandrian presbyter of the fourth century who first brought it into prominence. . . . Many of the leading men in England had become Arians, including Milton, Locke, . . . ; and the reading of their books in New England led to an inquiry into the truthfulness of the doctrine of the Trinity."

5. Locke is not entirely consistent in his definition of faith and at iv 17.24 defines it as "nothing but a firm assent of the Mind." Thus one can have this general kind of faith in the veracity of the gospel accounts of Jesus' miracles, which in turn can ground faith of the more specific kind in Jesus' claim that he was bringing a revelation of God.

6. Locke 1975, iv 16.13: "there is one case, wherein the strangeness of the Fact lessens not the Assent to a fair Testimony given of it. For where such supernatural Events are suitable to ends aim'd at by him, who has the Power to change the course of Nature, there, under such circumstances, they may be fitter to procure Belief, by how much the more they are beyond, or contrary to ordinary Observation. This is the proper Case of Miracles, which well attested, do not only find Credit themselves; but give it also to other Truths, which need such Confirmation."

7. In Locke 1965, section 143, Locke indicates that God only rarely uses miracles. "Though it be easy for omnipotent power to do all things by an immediate overruling will, and to make any instruments work, even contrary to their nature, in subserviency to his ends, yet his wisdom is not usually at the expense of miracles . . . but only in cases that require them for the evidencing of some revelation or mission to be from him. He does constantly (unless where the confirmation of some truth requires it otherwise) bring about his purposes by means operating according to their natures. If it were not so, the course and evidence of things would be confounded; miracles would lose their force and name; and there could be no distinction between natural and supernatural."


Aaron, Richard I. 1937 (rpt. 1955). John Locke. Oxford: Oxford University Press.

Chappell, Vere, ed. 1995. The Cambridge Companion to Locke. New York: Cambridge University Press.

Clapp, James Gordon, 1967. "John Locke." In The Encyclopedia of Philosophy. Ed. Paul Edwards. New York: MacMillan and Free Press. Vol. 4.

Cooke, George Willis, 1902. Unitarianism in America. Boston: American Unitarian Association.

Kane, R. H. 1995. "Socinianism." In Cambridge Dictionary of Philosophy. Ed. Robert Audi. Cambridge University Press.

Locke, John, 1956. The Second Treatise of Government and A Letter Concerning Toleration. Ed. with intro. by J. W. Gough. New York: MacMillan.

Locke, John, 1975. An Essay concerning Human Understanding, ed. Peter H. Nidditch. Based on original fourth ed., 1700. Oxford University Press.

Locke, John, 1965. The Reasonableness of Christianity as Delivered in the Scriptures. Chicago: Regnery Publishers.

McLachlan, Herbert, 1941. The Religious Opinions of Milton, Locke and Newton. Manchester University Press.

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