Evangelicalism is currently embroiled in a controversy of no small proportion. Authors we have looked to for years, whose counsel has elevated our Christian experience and deepened our understanding of ourselves and of God, have been branded as "heretics."
Why have these men been vilified? Because they promote principles gleaned from psychology and not specifically from the Bible, thus producing a poisonous amalgam of godless philosophy and biblical wisdom.
The Bible is fully sufficient, say critics like the Biblical Counseling Foundation. "The Word of God has been given to man as the sole source for finding God's solutions to the real problems that plague him."  (Emphasis mine.) The Foundation decries "futile attempts to mix God's Word with unregenerate suppositions and theories." 
It's hard to argue with the noble desire to focus on training materials that are more directly biblical. It's also possible that respected leaders in our midst can do us harm. Wolves come in sheep's clothing, Jesus warned.
Sometimes, though, the distinction between fleece and fur is not so easily determined. Even proof texts that seem crystal clear at first, take on a different sense when examined more closely or balanced against other Scriptural teaching.
I won't comment here on the role of psychology in the life of the Christian except to say I'm a centrist on the issue. I'm concerned with a more foundational idea: Is the Bible "sufficient" in the sense that these critics claim?
Scripture on the "Adequacy" of Scripture
"Bible only" advocates rely on a handful of references to prove that Scripture provides the sole solutions to life's problems. These three are characteristic:
"You shall not add to the word which I am commanding you, nor take away from it, that you may keep the commandments of the Lord your God which I command you" (Deuteronomy 4:2). 
"Do not add to His words lest He reprove you, and you be proved a liar" (Proverbs 30:6).
"And if anyone takes away from the words of the book of this prophecy, God shall take away his part from the tree of life and from the holy city, which are written in this book" (Revelation 22:19).
None of these verses teach what is claimed. The Deuteronomy passage only prohibits anyone from changing the specific revelation Moses has just given. Note that 61 additional books of the Bible were written after Moses penned these lines in the Pentateuch. The passage does not forbid the use of man's observations about life and human behavior.
The Proverbs passage simply says not to add to God's Word. No Christian I'm aware of, though, considers principles of psychology equal to Scripture in authority.
Revelation 22:19 forbids adding to the "words of the book of this prophecy," that is, the revelation itself. This verse is not even limiting the extent of the canon, much less excluding human wisdom about man's problems.
The passage in 2 Timothy 3:16–17 is more substantial.
2 Timothy 3:16–17
Paul writes in his last epistle, "All Scripture is inspired by God and profitable for teaching, for reproof, for correction, for training in righteousness; that the man of God may be adequate, equipped for every good work."
The reasoning of "Bible only" advocates goes something like this. Paul says that Scripture is adequate. If Scripture is adequate, then nothing more is required. If nothing more is required, then the use of outside material implies the inadequacy of the Bible, contradicting Paul's statement. Therefore, nothing in addition to Scripture can be used to equip us, because nothing else is "profitable for teaching, for reproof, for correction, for training in righteousness." This function is the sole province of the Bible.
That's the argument. Here's what's wrong with it. First, in the 2 Timothy passage the word "adequate" modifies the believer, not the Scripture. The words Paul uses to describe Scripture are "inspired" and "profitable." The Bible is useful to accomplish a certain end—an adequately equipped Christian—because it is the very counsel of God. Paul's teaching in Second Timothy was meant to qualify the nature of Scripture, not to disqualify the usefulness of other material.
Second, the argument proves too much. The Scripture Paul has in view is the Old Testament, specifically the sacred writings of Timothy's childhood (note verse 15). These are what Paul identifies as being able to "give you the wisdom that leads to salvation through faith which is in Christ Jesus."
If the Old Testament Scriptures are adequate, and if Paul means to suggest that the addition of any useful information about man is wrong, then how do we justify adding the words of the New Testament to the fully adequate Old Testament? Even Paul's words (as well as Peter's, John's, etc.) would be inadmissible, including the very words of 2 Timothy 3:16–17 which make this claim.
Since this is ludicrous and self-defeating, the entire objection crumbles. Paul did not mean to convey that other sources of knowledge were an assault on the Scripture's completeness.
Third, and more debilitating to this view, 2 Timothy 3:15 doesn’t even teach that the Scripture is adequate. A close look at the text reveals that the words “inspired” and “profitable” describe the Scripture. However, the word “adequate” does not describe the Scripture, but rather “the man of God” who uses the inspired Scripture in a profitable way. Note carefully: “...that the man of God may be adequate , equipped for every good work.” Once again, the proof text itself has unwittingly been maligned to say something it just doesn’t say, given the context.
What does "adequate" mean here? It probably means what adequate usually means, that the man of God has everything that is essential. Food and air and water are adequate to keep one alive, but their adequacy doesn't imply that nothing else is beneficial.
Some have pointed out that my argument could be used to teach that Paul thought only the Old Testament was inspired, not the New. Not so. Paul's statement was about Scripture, which at that time was what we now call the Old Testament. He did not say that no more "God-breathed" writings would be forthcoming. The corpus of Scripture was expanded by the New Testament writes and therefore it's included under the claims of this verse.
The problem only arises if one imposes a foreign sense of adequacy on this passage, i.e., nothing else is allowed. If we hold that Paul and the Apostles wrote legitimate Scripture, then that proves Paul's didn't intend such a restriction. That's my point.
Proverbs and Wisdom from Nature
There are other problems with the "Bible only" view. Scripture itself seems to encourage us to take counsel from other sources of information. The mandate to be fruitful and multiply in Genesis seems to require that man observe his environment, learn useful things, and then employ them to improve his condition—all apart from direct revelation.
This is precisely what we find in the book of Proverbs. According to Solomon, wise counselors are those who are skilled at life, including the ability to observe the natural realm and deduce spiritual truth, moral knowledge, and skills at living.
Note this statement in Proverbs 24:30–34:
I passed by the field of the sluggard, and by the vineyard of the man lacking sense; and behold, it was completely overgrown with thistles. Its surface was covered with nettles, and its stone wall was broken down. When I saw, I reflected upon it; I looked, and received instruction . "A little sleep, a little slumber, a little folding of the hands to rest," then your poverty will come as a robber, and your want like an armed man.
Dr. John Coe, professor of psychology at Rosemead University, has this to say about Proverbs 24:
Though the sage elsewhere acknowledges the Scriptures as a source of wisdom (Prov. 29:18), here he informs us that his own reflections and observations were sufficient to gain this piece of practical and moral wisdom. In fact, this pattern seems to fit well with many of his proverbs which do not explicitly depend upon the Torah or some further divine revelation. Thus, it seems reasonable to conclude that the sage's peculiar task, in contrast to the priest and prophet, involves keenness in observation and reflection for interpreting natural, particularly human phenomena. His reflections result not only in the theoretical and technological knowledge for the natural sciences, but especially in moral knowledge for the human sciences (viz. the Proverbs ). In the above case the sage, on the basis of observation and reflection, discovers that laziness leads to financial ruin and self-injury.
The sage, then, is convinced that by observing and reflecting upon the ordering structures particularly of the human situation he will discover quasi-causal laws which govern the human situation. From these observations he claims to receive instruction and wisdom for living, hence, moral knowledge.  [Emphasis in the original.]
Dr. Coe's point is an important one. Proverbs 24:30–34 shows that we can draw true conclusions about right conduct through astute observations of the world. Even before the sage says, "My son, observe the commandment of your father" (6:20), he says, "Go to the ant, O sluggard. Observe her ways and be wise" (5:6).
The Scriptures in general, then, find their authority in the fact that they are given by God. However, the Scriptures recognize another source of wisdom as well, to which the OT sage appeals for his wise principles. Of course, as a member of the believing community the Hebrew sage recognizes that God is the ultimate source of all wisdom (2:6), that a relationship with Him is requisite for a fully wise life (1:7), and that the Scriptures are necessary for the mental health of a community (29:17, 30:5–6). However, as a member of a community of sages he ventures out into the natural order of things—with Scriptures in hand and God in mind—in order to discern the wisdom available as well in natural and human phenomena.  [Emphasis in the original.]
Dr. Coe argues that God's will is expressed in propositional form (Scripture) and non-propositional form (nature). Through observation and reflection on either—if they are properly interpreted—one can infer principles for living because both inform man how to live well.
Taking his own advice, the sage of Proverbs makes this observation:
Four things are small on the earth, but they are exceedingly wise: the ants are not a strong folk, but they prepare their food in the summer; the badgers are not mighty folk, yet they make their houses in the rocks; the locusts have no king, yet all of them go out in ranks; the lizard you may grasp with the hands, yet it is in kings' palaces (30:24–28).
Consider this scenario. When a city is plagued by violence, the people decide to execute murderers. Immediately the murder rate drops and peace is restored to the city. These people used their fallen, human wisdom to employ a biblical solution—government bearing the sword to mitigate the impact of evil. They accurately assess and solve a human problem, even with no knowledge of Scripture. This kind of thing happens all the time.
Wisdom from the Heathen
The Wisdom Literature of the Amenomope is a body of work from the Middle East that pre-dates Proverbs. It's of interest because it contains a section of material almost identical to Proverbs 22:17–24:22. It seems evident that the authors of the latter part of Proverbs borrowed this material from the Amenomope and inserted it into the inspired text.
Some scholars see this as a serious compromise of the doctrine of inspiration. However, a more robust (and, I would say, more biblical) view of natural theology removes the objection. Clearly, natural man apart from God is capable of discerning truth that, according to the writer of Proverbs, is from God.
Paul's classic teaching in Romans 1:18ff identifies the universal, innate ability to draw conclusions about God's nature without the aid of special revelation—a capability so effective that the willful suppression of it brings God's judgment.
Keep in mind that the specific details Paul identifies here—"His invisible attributes, His eternal power and divine nature"—are only examples of natural revelation, not the total sum of it. He doesn't limit our knowledge to only basic information about God's existence.
In Genesis 18:25, Abraham challenges God's plan to destroy Sodom and Gomorrah: "Far be it from Thee to do such a thing, to slay the righteous with the wicked, so that the righteous and the wicked are treated alike. Far be it from Thee! Shall not the Judge of all the earth deal justly?" Where did Abraham get his notion of justice? It was innate, natural revelation, a moral law built into his humanity.
One thing at stake here is natural theology—that which can be known about God and about man's spiritual condition through general revelation. Can unregenerate man know anything significant without the aid of special revelation? The Bible seems to teach he can know much.
Knowledge from Natural Revelation
The late Dr. Francis Schaeffer pointed out, the Bible is true truth, but not exhaustive truth. It's completely true about everything to which it speaks, but it doesn't speak about everything there is to know. Much more can be discovered.
Dr. Bruce Demarest, Professor of Systematic Theology at Denver Seminary, makes this observation:
Although man is a sinner, he uniquely bears the image of God. The crippling effects of sin in the human mind are overcome in part by a general illumination of the Logos (John 1:4, 9). God wills that man, the pinnacle of His creation, should use his reason to secure truth, including elementary truths about himself. Equipped with an intuitional knowledge of God, including the light of conscience, and enabled by common grace, man by rational reflection on the data of the natural and historical order draws inferences about God's character and operations. By inspection of the created order that surrounds him and by the discursive workings of the mind by which one thing is inferred from another, man reaches conclusions that confirm the fact of God's existence and enlarge his understanding of the character of the Creator, Preserver and Judge that stands over him. 
Man, made in the image of God, gains knowledge based on general revelation. He has an innate ability to know first principles and basic rules of logic, Demarest argues, and knows how to apply these abilities to learn truth, not just about his world, but also about spiritual things.
Demarest concludes, "Scripture supports our thesis that further truth content about God is acquired by rational reflection on God's general revelation on nature in history." 
A case in point is Dr. Bernard Nathanson. An atheist, he was one of the founders of the National Abortion Rights Action League (NARAL). Nathanson ran one of the largest commercial abortion operations in the country. He later repudiated the practice and has become an ardent advocate of the rights of the unborn child.
Why the change of heart? Because he became convinced that abortion was a serious violation of human dignity.
The irony is that Bernard Nathanson remained an atheist. One could argue it's very hard to justify the concept of human rights—a type of transcendent law—if there is no God. Nathanson's reversal, however, proves that even those with faulty philosophical foundations (like Freud, Maslow, Jung, etc.) can reason inconsistently to a conclusion that turns out to be true. Nathanson's thinking is inconsistent with his world view, but his intuitive knowledge of human value—a function of general revelation—is correct. 
The View of the Reformers
Even the Reformers, aggressive in asserting total depravity and advocates of sola Scriptura , did not hold to this radical version of "Bible only." Note Calvin:
In reading profane authors, the admirable light of truth displayed in them should remind us, that the human mind, however much fallen and perverted from its original integrity, is still adorned and invested with admirable gifts from its Creator.... How then can we deny that truth must have beamed on those ancient lawgivers who arranged civil order and discipline with so much equity? Shall we say that the philosophers, in their exquisite researches and skillful description of nature, were blind? ... Therefore, since it is manifest that men whom the Scriptures term natural, are so acute and clear-sighted in the investigation of inferior things, their example should teach us how many gifts the Lord has left in possession of human nature, not withstanding of its having been despoiled of the true good. 
Calvin does not take lightly this "despoiling." Regarding spiritual discernment—"the knowledge of God, the knowledge of...our salvation and the method of regulating our conduct in accordance with the Divine Law"—he said that "the mind of man must ever remain a mere chaos of confusion. To the great truths, what God is in Himself, and what He is in relation to us, human reason makes not the least approach." 
Calvin distinguished between two kinds of knowledge. He calls them natural gifts and supernatural gifts. Calvin holds, with Augustine, that man's natural gifts were corrupted by sin, but not withdrawn.  He then continues for almost five pages in his Institutes detailing the capabilities of fallen reason.
According to Calvin, only man's supernatural gifts were lost, specifically "the light of faith and righteousness, which would have been sufficient for the attainment of heavenly life and everlasting felicity." 
Would this great Reformer condemn the contributions of modern psychology as mere worldly wisdom? No, that's all part of the natural gifting God has given to man. Calvin even extols what he calls the shrewd observations of Aristotle:
Aristotle seems to me to have made a very shrewd distinction between incontinence and intemperance. Where incontinence reigns, he says, that through the passion particular knowledge is suppressed: so that the individual sees not in his own misdeed the evil which he sees generally in similar cases; but when the passion is over, repentance immediately succeeds. 
The broader context of this passage makes Aristotle's point clearer. People have a tendency to acknowledge general moral principles, but go into denial when they personally contemplate committing sin. Afterwards, guilt and remorse set in.
Whether one agrees with the particular point or not is incidental. What is important is that John Calvin—a principal Reformer utterly dedicated to the biblical doctrine of "total depravity" —quotes an unregenerate Greek philosopher on the vicissitudes of the human psyche. Calvin is using Aristotle's psychology to help articulate an aspect of man's fallenness.
The question "Is Scripture adequate?" is much like the question "Is Christ adequate?" The answer depends entirely upon what one expects either to do. Each one does something specific for us; neither does everything. In one sense, God wasn't even adequate for Adam in the garden. Though Adam was walking in unfallen fellowship with the Father, God still said, "It is not good for the man to be alone; I will make him a helper suitable for him" (Genesis 2:18).
The Bible is sufficient to give the "wisdom that leads to salvation" and to enable the godly person to be "adequate, equipped for every good work" (2 Timothy 3:15,17). Such sufficiency does not preclude other sources of learning that give further instruction in mental health and skill at living.
The Scripture is the standard of truth to be studied, applied, and cherished. The Bible itself, however, doesn't support the "Bible only" view. It does not teach that man is so distorted by sin as to lose his ability to discover useful truth on his own. It teaches rather that man has an extensive ability to draw from general revelation making accurate and useful assessments about life and its problems.
Christians who, however well-intended, promote this narrow view, encourage unnecessary conflict in the church. They also deny believers a source of wisdom and knowledge the Bible itself encourages us to consider.
 Broger, John C., Self-Confrontation syllabus (Rancho Mirage, CA: Biblical Counseling Foundation, 1991).
 It's not clear what "unregenerate suppositions and theories" are, except possibly those suppositions or theories coming from unregenerate people. Ideas and theories aren't the subjects of regeneration; people are. Why is a theory false, though, simply because it comes from an unregenerate person? Would the same theory coming from a believer be true?
 All Scripture quotations are from the New American Standard Bible .
 "Why Biblical Counseling is Unbiblical, or Speaking Psychology Gently into the Church," Dr. John Coe, p. 20–21; from a paper read at the 1991 Evangelical Theological Society, Far West Regional Annual Meeting (paper on file).
 Ibid . , p. 26–27.
 Bruce Demarest, General Revelation: Historical Views and Contemporary Issues (Zondervan: Grand Rapids, 1982), p. 233.
 Ibid., p. 234.
 Incidentally, it's my understanding that Nathanson has since become a Christian.
 Institutes , Book II, ch. 2, para. 15.
 Ibid., para. 18.
 Ibid., para. 12.
 Ibid., para. 23.
 "Total depravity" is the accepted term, but I've put it in quotes because it's actually a misnomer, giving the mistaken impression that man is incapable of producing anything good or of value. Our term "total depravity" actually means that no part of man is untouched and untainted. The extent of the impact of the fall is total, not the degree .