Post Publication note: Originally, this article was written specifically to address Sola Scriptura from a Catholic perspective. However, Catholics are not the only heretics to deny Sola Scriptura, nor does Sola Scriptura need Catholic opposition to exist. Therefore, while I have chosen to leave the article mostly unedited, the same case may be used against all heretics who deny Sola Scriptura, though obviously with Catholic-specific arguments removed.
Sola Scriptura is the belief that Scripture contains all things necessary for faith and the manner of life. Where Christians believe that the Bible is all a Christian ever needs for doctrine, and is the sole infallible authority (though not necessarily the sole authority full stop). Catholic dogma is that both "sacred" tradition and Scripture are to be accepted and venerated with the same sense of loyalty and reverence (1).
Catholics often argue that as Sola Scriptura is, itself, not found in the Scriptures, and thus is not only false, but self refuting. This is because they typically don't understand, whether through a lack of knowledge, or through deliberate ignorance, what Sola Scriptura actually is. They so often claim it's not in Scripture because they don't know what they're looking for. So, it is only fitting that we examine and expound upon what Scripture says about its own authority, and show how Sola Scriptura, not the Catholic view of authority, is the only viable model.
"Ye shall not add unto the word which I command you, neither shall ye diminish ought from it, that ye may keep the commandments of the Lord your God which I command you."
- Deuteronomy 4:2
Here, the Lord clearly tells Israel that adding to, or removing from His words, which the Catholic Church does frequently, will inevitably result in disobedience, and thus commands that this not be done. This isn't just an empty threat. There are multiple times recorded in Scripture wherein someone did add to, or remove from, the word of God, resulting in some form of disobedience. In fact, adding to the word of God is one of the first philosophical failures of the human race. Eve told Satan that God had commanded "Ye shall not eat of it, neither shall ye touch it, lest ye die." (Genesis 3:3), but the real command was "...but of the tree of the knowledge of good and evil, thou shalt not eat of it: for in the day that thou eatest thereof thou shalt surely die." (Genesis 2:17). There was nothing about touching it, and so when Eve touched the fruit and did not die, Satan had everything he needed to cast doubt on God's word.
But Eve's example is only implicit. The Scripture implies that her addition gave an advantage to Satan, but it doesn't explicitly say "For laying aside the commandment of God, you hold the tradition of Eve...". What the Bible does say, however, is "For laying aside the commandment of God, ye hold the tradition of men (...)". This quote, from Mark 7:8, is part of an event that is recorded twice in the Gospels, the first being in Matthew 15:1-9 and the second being in Mark 7:1-13. Both accounts have several things in common, namely the Pharisees, who were effectively the Jewish version of Catholics, had their own traditions, which they preached as authoritative. This resulted in their disobedience to God's explicit commands. Specifically, Jesus called them out for elevating giving gifts to God above the command to honor your parents.
Just as the Pharisees elevated their traditions above the commands of God, so also do Catholics elevate their traditions above the Scriptures. But it doesn't stop there: They also remove from the word of God. An ironic example is Canon 6 of the 1983 Code of Canon Law, which actually states that anything in the Code of Canon Law 1917 that was not renewed in 1983 has since been "abrogated" (2). Why is this ironic? Because Code of Canon Law 1917 mandated women wear head coverings in church, in step with 1 Corinthians 11:2-16. Verse 2 specifically says "Now I praise you, brethren, that ye remember me in all things, and keep the ordinances, as I delivered them to you." (KJV, but more modern translations render the word "ordinances" as "traditions"). Because of that word "traditions", verse 2 is a popular verse for Catholics to cite when defending their idea of authoritative traditions. It is ironic that a verse so frequently cited to prove that traditions are authoritative concerns a tradition that not even the Catholic Church regards as authoritative!
As a final note before we move on, I wish to highlight a misunderstanding that springs from the aforementioned verse about traditions. Sola Scriptura does not necessarily discount all traditions, but rather puts tradition in its proper place. There are three main categories of tradition: Scriptural, extra-Biblical and anti-Biblical. Of course scriptural traditions are authoritative! You can't believe Sola Scriptura without believing Scripture is authoritative. So, the fact that the Scriptures specifically describe a tradition as authoritative does not prove all traditions are authoritative. Indeed, not even the Catholic Church would believe it does. There are a great many traditions that not even the Catholic Church would accept. Case in point? Sola Scriptura! Sola Scriptura is a tradition, and ironically it was taught by the same Paul who wrote 1 Corinthians, meaning "Protestants" are actually more faithful to the traditions of Paul than Catholics are.
Extra biblical traditions are entirely optional. They are binding only upon the individual that binds themselves to them, but not upon the whole Church. To quote Jerome, "that which hath not authority from scripture, we can as easily despise as approve." (3). Needless to say, anti-biblical traditions, like several seen in the Catholic Church, have authority from Satan, not from God. God cannot deny Himself (2 Timothy 2:13), and so He also cannot give conflicting traditions. When a tradition conflicts with Scripture, it conflicts with God, and must be discarded under all circumstances.
"Every word of God is pure: he is a shield unto them that put their trust in him. Add thou not unto his words, lest he reprove thee, and thou be found a liar." - Proverbs 30:5-6
First off, it is very telling that the Scriptures repeatedly affirm the purity of God's words, but not once does it say the same about any man. The extreme fallibility and even depravity of our species is a central theme in the Bible, so how can any man possibly be considered infallible? But the Catholic Church adds a lot of man's word to God's. An excellent example is Matthew 16:18-19. According to First Vatican Council, Peter, "in his single person, preferably to all the other Apostles, whether taken separately or together, was endowed by Christ with a true and proper primacy of jurisdiction..." (4) It even goes as far as to say "If anyone, therefore, shall say that Blessed Peter the Apostle was not appointed the Prince of all the Apostles and the visible Head of the whole Church Militant; or that the same, directly and immediately, received from the same, Our Lord Jesus Christ, a primacy of honor only, and not of true and proper jurisdiction; let him be anathema." The above isn't just an addition to the Scriptures, but it is also in opposition to the Scriptures.
But in declaring that the Church has ever understood this to be the case, First Vatican Council made a demonstrably false claim. As it turns out, historically speaking, Peter being the ROCK was a minority interpretation even amongst the Church "Fathers", much less the Pope! And so, by adding to the scriptures, the Catholic Church is, indeed, often shown to be a liar.
"Surely the Lord God will do nothing, but he revealeth his secret unto his servants the prophets." - Amos 3:7
Aside from adding doctrine to the Scriptures, the Catholic Church also adds a number of fables. As an example, there is the immaculate conception and bodily assumption of Mary. According to Catholicism, Mary was unique among humanity in that she was born without original sin. She was also one of only four people to be bodily assumed into Heaven (Enoch, Elijah and Jesus being the other three).
A noteworthy thing about the Old Testament is that it is absolutely flooded with Messianic prophecies. The New Testament also has several references to Old Testament prophecies which had been fulfilled in the surrounding verses. Almost every aspect of Jesus' life, including His virgin birth in Bethlehem, His miracles, His suffering, His betrayal by Judas, the fact that His brothers would disown Him (which is another error in the Catholic Church, which preaches Mary's perpetual virginity, and thus that Jesus could not have had brothers), all of this and more is clearly visible in the Old Testament. But no matter how hard you look, you will never find a single prophecy about a woman who is uniquely conceived free of original sin, or assumed bodily into Heaven. If the Lord does nothing without revealing His secrets to His prophets, and He did not reveal to His prophets the secret that Mary would be born without original sin or bodily assumed into Heaven, the logical conclusion is that the Lord did nothing miraculous with regard to Mary's conception, nor her death.
Additional myths about Mary are just one example, but ultimately, Amos 3:7 shows us that if God is going to do something, He's going to tell a prophet. This doesn't necessarily mean Scripture will record it, but it does strongly suggest that, as the only confirmed prophetic writing, Sola Scriptura is, at the very least, a very good rule of thumb.
"And these things, brethren, I have in a figure transferred to myself and to Apollos for your sakes; that ye might learn in us not to think of men above that which is written, that no one of you be puffed up for one against another." - 1 Corinthians 4:6
To be as generous as possible to the Catholic Church, it must be noted that the rendering of this verse varies between translations. Most of them say some variation of "do not think beyond what is written" ("it is written" being the way scripture refers to itself). But the KJV (ironic that using the KJV is being generous to the Catholic) renders it "not to think of men above what is written". This rendering also fits the context of the passage in question, so we'll roll with this.
Now, if we are not to think of men beyond what is written, what does that say about the numerous times in which the Catholic Church thinks of men beyond what is written? The Catholic Church has ecclesiastical roles that do not exist in the Bible, or that are different, sometimes radically, from the equivalent Biblical role. It also elevates several Biblical figures to positions they never had. The Bible never says Peter was the supreme Apostle. The Bible never says Mary is the Queen of Heaven. The Bible never describes cardinals or an archbishop. The Bible says that all believers are priests (1 Peter 2:9), and literally describes the celibacy of the clergy as a "doctrine of devils" (1 Timothy 4:1-3). In other words, even if we are as generous as possible to the Catholic and say that it only defends Sola Scriptura as far as people's roles are concerned, 1 Corinthians 4:6 is an excellent Sola Scriptura verse that simultaneously refutes the Catholic authority structure!
"All scripture is given by inspiration of God, and is profitable for doctrine, for reproof, for correction, for instruction in righteousness: That the man of God may be perfect, thoroughly furnished unto all good works." - 2 Timothy 3:16-17
2 Timothy 3:16-17 is, by far, the best verse to use when demonstrating Sola Scriptura, as it literally describes it, word for word and in great detail. It is so perfect that you can quote it at a less experienced Catholic, not tell them what you're quoting, and they will deny that it's true. Unfortunately, as effective as it is, it is also well known, so Catholics have developed a number of attempted counter-arguments.
The first attempt at a counter argument is that the Catholic Church also believes the Bible is inspired, and is useful for doctrine, for reproof, for correction, and for instruction in righteousness. In other words, they claim that 2 Timothy 3:16-17 is not a valid refutation of their beliefs because they already believe it. But they actually don't, because although they believe everything described in verse 16, they do not believe in verse 17, which says that the purpose of all of the above is "that the man of God may be complete, thoroughly equipped for every good work."
The word "complete" means having everything necessary or appropriate. "Every" means all possible. No exceptions. Thus, if the Bible makes us complete, we have everything necessary or appropriate to be men of God in the Scriptures. If the Scriptures thoroughly equip us for every good work, there are no good works for which we can possibly be unequipped if we know the Scriptures. And yet the Catholic Church has a range of wild and wacky additions, including what it claims are "good works". The whole concept of confession, for example, is unBiblical. The Catholic Church even distinguishes between "mortal" and "venial" sins, which the Bible not only fails to do, but actually explicitly teaches the opposite (James 2:10). This makes the entire Catholic concept of sin very different from what is described in the Bible. All of this means that although Catholics must claim that the Bible is inspired, they must reject the idea that it makes a man of God complete or equips us for every good work.
The second attempt to counter this verse is to back up a few verses (which I honestly wish Catholics would do more often) and say that because verses 14-15 show that Paul is referring specifically to the Scriptures Timothy was familiar with from his childhood, the passage must not be referring to the New Testament, but only to the Old. This is the only time I am aware of when Catholics will actually distinguish between the Old and New Testament like this, and for good reason. As I previously pointed out, both Catholics and Christians believe the entire Bible is inspired. Catholics are correct to agree on the New Testament, because when Paul said all Scripture is inspired by God (literally "God breathed", as we will address in a moment), he meant it.
It should first be noted that 2 Timothy is not the earliest New Testament book to be written. It is generally believed to have been written around 66-67 A.D., putting it behind a number of books. Although it is not confirmed, it may have been written after 2 Peter (between 65-68 A.D.). This is especially significant to this argument, because in 2 Peter 3:16, Peter identifies Paul's epistles as being authoritative Scripture, which would mean Peter knew 2 Timothy is Scripture. But even if we assume 2 Peter was written after 2 Timothy, the very title of 1 Timothy should clue us in to the fact that it certainly wasn't. Yet in 1 Timothy 5:18, Paul says "For the scripture saith, thou shalt not muzzle the ox that treadeth out the corn. And, The labourer is worthy of his reward." This is significant, because that means Luke (10:17) was both in existence and counted as equal Scripture with Deuteronomy 25:4.
When Paul wrote in 2 Timothy 3:16 that all scripture is inspired, he never distinguished between the Old Testament Scriptures that had existed since 400 B.C. and the Scriptures that were coming into existence during his time. This also invalidates the Catholic Church's attempt to claim they are responsible for the recognition of the canon via the councils of Rome, Hippo, or Carthage, since the Catholic Church had not yet formed, and the Councils had not yet been held, yet Paul already recognised Luke as Scripture, and clearly Timothy did too. Thus, 2 Timothy 3:16-17 must necessarily have meant all scripture, which Peter and Paul, and evidently anyone under their authority, did not wait for Carthage to recognise.
"Knowing this first, that no prophecy of the scripture is of any private interpretation. For the prophecy came not in old time by the will of man: but holy men of God spake as they were moved by the Holy Ghost." - 2 Peter 1:20-21
This relates to earlier when we spoke about the fallibility of men vs. the infallibility of God. I said that the human traditions of the Catholic Church cannot be authoritative because they did not come from God, but men. The obvious response would be "but the Scriptures were also written by men". This comes back to the whole "God breathed" concept mentioned above. Although the Scriptures were physically written by men, they were directed by God, meaning whatever parts of their human authors did shine through in the Scriptures is still infallible.
Not so with Catholic tradition, which we've amply demonstrated is often factually wrong. I was rather amused when I cited this verse to a Catholic once, and he tried to flip it on me by saying that 2 Peter 1:20-21 actually proves Catholicism, because it says you can't interpret the Bible. But what it actually says is that the scriptures were not written by private interpretation, not that men are incapable of interpreting it correctly while reading it. When a Christian reads the Bible, he's not reading a private interpretation, unlike when reading a false work, such as when Joseph Smith claimed he would personally dedicate the New Jerusalem in Missouri. When the prophets were writing the prophecies, the prophecies didn't come from them, but from God.
Catholicism, by contrast, is well known for such private interpretations. A famous example is Galileo, who was tried for heresy. His crime? He believed the earth revolved around the sun rather than vice versa. Now, the Catholic Church has since apologised for this (not that it makes a difference, the damage is done, and he can't exactly pop up and say "it's cool"), but especially historically, the Catholic Church is riddled with the kind of private interpretations Peter is saying Scripture does not come from. The very fact that an apology needed to be made indisputably proves the human error involved here. By contrast, when did Jesus ever apologise for His judgements?
But even today there is a lot of speculation in the Catholic Church. Take, for example, the concept of canonised Saints. A Saint is someone who, according to the Catholic Church, is definitely in Heaven, and can even be prayed to, or asked for prayer because they (allegedly) have a more direct access to God. Which, I might add, the Bible says is not true because we can boldly approach the throne of grace (Hebrews 4:16), whereas communicating with the dead is an abomination (Deuteronomy 18:11-12), and we should instead seek God Himself, because it is not fitting for us to consult the dead on behalf of the living (Isaiah 8:19-20). Isaiah even says you have no light in you if you say anything else than "to the law and testimony".
Thus, by breaking the law and testimony and consulting the dead rather than the Lord on behalf of the living, Catholics show there is no light in them. The Bible does give us a lot to go on when it comes to figuring out where the dead are. We know for a fact Judas is going to Hell (Matthew 26:24; John 17:12). We know that the thief on the cross is in Paradise (Luke 23:43). The professed faith of the dead during their lives gives us a good indication as to whether or not they shared either man's fate. Unbelievers, barring a deathbed conversion, are doomed, and believers, barring a false conversion, are saved. But even knowing our own eternal fate (1 John 5:13) does not grant us the ability to definitely say "yes, that person is in Heaven". Only God can see the heart. An extra layer to add to Catholicism is that they believe (falsely, according to Romans 8:1, Hebrews 9:27, and 2 Corinthians 5:8) in Purgatory, which means even if they believe someone had true faith, they don't know that such a person is in Heaven instead of Purgatory. They just assume they do.
Amusingly, St. Mark Ji Tianxiang was denied the Eucharist for 30 years because of an opium addiction, which was considered by his priest to be a mortal sin because he kept doing it, suggesting his confession did not stem from a desire to repent (they didn't understand addiction back then). (Update: I have since found out that many Catholic saints had similar experiences with being denied the Eucharist, and dying without it). Catholics often misinterpret John 6:48-62 as referring to the Eucharist. Verse 53 especially says "Then Jesus said unto them, Verily, verily, I say unto you, Except ye eat the flesh of the Son of man, and drink his blood, ye have no life in you." Now, of course Jesus is speaking spiritually in John 6:48-62. In verse 63, He explicitly says so, and let's not forget that verse 47 tells us that "eating" Jesus' flesh and blood actually refers to our belief in Him. So, when verse 53 says we must eat the flesh of the Son of Man and drink His blood, or we have no life in us, Jesus is saying you must believe in Him to be saved. No one in the Bible ever referred to the bread and wine as literally being Jesus' flesh and blood, and Peter even stubbornly refused to eat anything "common and unclean", which would include human blood, in Acts 10:14. But just for the moment, we'll suspend every rule of hermeneutics and just assume that the Catholic interpretation is correct and John 6 really does talk about the Eucharist (a moment while I puke about the cannibalistic implications). Now, if you have no life in you if you don't eat the flesh and blood of Christ, and Catholics of course do this thousands of times over during their lives, it makes sense that St. Mark Ji Tianxiang had no life in him. Thus, even if we take Catholicism seriously, Tianxiang should be in Hell paying for his mortal sin. Thus, by canonising him, they're not only privately interpreting Tianxiang's eternal fate in reality, but that private interpretation even contradicts the view of salvation in the Catholic faith!
"Beloved, when I gave all diligence to write unto you of the common salvation, it was needful for me to write unto you, and exhort you that ye should earnestly contend for the faith which was once delivered unto the saints." - Jude 1:3
While Christianity was already complete in the first century, never to change, Catholicism constantly evolves. Councils not only add, or officially endorse new doctrines, but doctrines can even be "abrogated". How can a faith that was delivered once for all in the first century be repeatedly changed throughout the ages? When debating Catholics, I find they frequently appeal to later authors. Clement, Ignatius, Augustine, even people as late as Aquinas. But as I always say, Catholics appeal to the early sources, Christians appeal to the earliest source. The reason Catholics devote so much time to extra-Biblical sources is because they know the Bible doesn't support their faith. The whole debate over Sola Scriptura stems from the fact that taking the Bible alone, no one would ever become Catholic. Catholicism simply cannot stand the test, because while the Christian faith was delivered once for all in the first century, the Catholic faith didn't even show up until at least 390 A.D., and it didn't become what it is today until much much later. Thus, while Jude 1:3 does not specifically show Scripture alone is the authority, it does disarm the authority of any tradition that evolved later. Since the Bible is the earliest Christian source, it just makes sense to use it to understand the faith as opposed to anything written in 100 A.D. or later.
"For I testify unto every man that heareth the words of the prophecy of this book, If any man shall add unto these things, God shall add unto him the plagues that are written in this book: And if any man shall take away from the words of the book of this prophecy, God shall take away his part out of the book of life, and out of the holy city, and from the things which are written in this book." - Revelation 22:18-19
Strictly speaking, this is the weakest of the Sola Scriptura verses, because it only covers the entirety of Scripture when the entirety of Scripture is compiled into one book. Although the early Church did recognise Scripture, it took a few decades to compile it into one, with Revelation being a disputed work. Thus it is semi-legitimate to say that Revelation 22:18-19 only applies to Revelation. However, two things must be taken into account. First, when God was inspiring Scripture, He knew full well it would eventually be compiled into one helpful volume for most of history. 90 years without being compiled into a book vs. more than 1800 years being in a book, it's reasonable to assume God intended it to cover all Scripture, just as 2 Timothy 3:16-17 does.
Second, in light of all the previous Scriptures (and indeed, Scripture should always be considered as a whole, no verse should be removed from that context), it just makes sense. We've already shown that adding to/removing from the word of God results in serious problems, so even if we only apply Revelation 22:18-19 to the rest of Revelation, we still have explicit commands not to add to or remove from His words. It's not like Revelation is a special, especially sacred Scripture intended to be treated as Holier than every other book. God won't throw up His hands and say to a Mormon "I know you discount the entire book of Song of Solomon, but at least you didn't omit a word of Revelation, so I'll give you a pass on that".
Conclusion
With all of the above, it is simply impossible to say that Sola Scriptura is not taught in the Scriptures. But we do see a clear motive for Catholics to continue to preach this lie. Sola Scriptura itself is a Biblical doctrine that Catholics oppose, but even if we pretend that Sola Scriptura is not a doctrine, the Catholic Church continuously develops new and unBiblical doctrines. So why wouldn't Catholics say things like "Sola Scriptura is the worst cancer on earth" (a genuine comment I once received)?
Imagine an earthly king. Imagine that king wrote a law book that repeatedly stated things like "don't add to this book or remove from it" and "I wrote this book, and it's useful to make you a complete citizen, thoroughly equipped for everything legal". How likely would he be to execute a citizen who swore by that book, even refusing to obey a supposed law firm that repeatedly did things not found in that book, or even did things clearly forbidden by it? The obvious answer is not likely at all. That citizen would be an upstanding citizen, whereas the law firm that messes with the book would have a few crimes to answer for.
God is the same. If you rely solely on His word, which consistently affirms its own sufficiency, He will look favorably on you, and if you disobey those who disobey Him, the disobedient will be the ones who receive judgement for that disobedience, whereas you will be spared. Catholics make so many excuses as to why their Church has authority over the Bible, but not only does the Bible tell us to test all things (1 Thessalonians 5:21), but it even contains an example of just that. In Acts 17:11, Paul and Barnabas preach the Gospel to some Jews in Berea, and they test his claims against the Scriptures. But the Catholic Church even forbids you to do that. Do it anyway.
References
1. DOGMATIC CONSTITUTION ON DIVINE REVELATION, DEI VERBUM (Link)
2. Code of Canon Law, Book 1, GENERAL NORMS LIBER I. DE NORMIS GENERALIBUS (link)
3. Commentariorum in Evangelium Matthaei [PL 26.180] on Mt. 23:35, 36
4. First Vatican Council, ON THE INSTITUTION OF THE APOSTOLIC PRIMACY IN BLESSED PETER (Link)