The word salafi or "early Muslim" in traditional Islamic scholarship means someone who died within the first four hundred years after the Prophet (Allah bless him and give him peace), including scholars such as Abu Hanifa, Malik, Shafi'i, and Ahmad ibn Hanbal. Anyone who died after this is one of the khalaf or "latter-day Muslims".
The term "Salafi" was revived as a slogan and movement, among latter- day Muslims, by the followers of Muhammad Abduh (the student of Jamal al-Din al-Afghani) some thirteen centuries after the Prophet (Allah bless him and give him peace), approximately a hundred years ago. Like similar movements that have historically appeared in Islam, its basic claim was that the religion had not been properly understood by anyone since the Prophet (Allah bless him and give him peace) and the early Muslims--and themselves.
In terms of ideals, the movement advocated a return to a shari'a-minded orthodoxy that would purify Islam from unwarranted accretions, the criteria for judging which would be the Qur'an and hadith. Now, these ideals are noble, and I dont think anyone would disagree with their importance. The only points of disagreement are how these objectives are to be defined, and how the program is to be carried out. It is difficult in a few words to properly deal with all the aspects of the movement and the issues involved, but I hope to publish a fuller treatment later this year, insha'Allah, in a collection of essays called "The Re-Formers of Islam".
As for its validity, one may note that the Salafi approach is an interpretation of the texts of the Qur'an and sunna, or rather a body of interpretation, and as such, those who advance its claims are subject to the same rigorous criteria of the Islamic sciences as anyone else who makes interpretive claims about the Qur'an and sunna; namely, they must show:
Only when one has these qualifications can one legitimately produce a valid interpretive claim about the texts, which is called ijtihad or "deduction of shari'a" from the primary sources. Without these qualifications, the most one can legitimately claim is to reproduce such an interpretive claim from someone who definitely has these qualifications; namely, one of those unanimously recognized by the Umma as such since the times of the true salaf, at their forefront the mujtahid Imams of the four madhhabs or "schools of jurisprudence".
As for scholars today who do not have the qualifications of a mujtahid, it is not clear to me why they should be considered mujtahids by default, such as when it is said that someone is "the greatest living scholar of the sunna" any more than we could qualify a school-child on the playground as a physicist by saying, "He is the greatest physicist on the playground". Claims to Islamic knowledge do not come about by default. Slogans about "following the Qur'an and sunna" sound good in theory, but in practice it comes down to a question of scholarship, and who will sort out for the Muslim the thousands of shari'a questions that arise in his life. One eventually realizes that one has to choose between following the ijtihad of a real mujtahid, or the ijtihad of some or another "movement leader", whose qualifications may simply be a matter of reputation, something which is often made and circulated among people without a grasp of the issues.
What comes to many peoples minds these days when one says "Salafis" is bearded young men arguing about din. The basic hope of these youthful reformers seems to be that argument and conflict will eventually wear down any resistance or disagreement to their positions, which will thus result in purifying Islam. Here, I think education, on all sides, could do much to improve the situation.
The reality of the case is that the mujtahid Imams, those whose task it was to deduce the Islamic shari'a from the Qur'an and hadith, were in agreement about most rulings; while those they disagreed about, they had good reason to, whether because the Arabic could be understood in more than one way, or because the particular Qur'an or hadith text admitted of qualifications given in other texts (some of them acceptable for reasons of legal methodology to one mujtahid but not another), and so forth.
Because of the lack of hard information in English, the legitimacy of scholarly difference on shari'a rulings is often lost sight of among Muslims in the West. For example, the work Fiqh al-sunna by the author Sayyid Sabiq, recently translated into English, presents hadith evidences for rulings corresponding to about 95 percent of those of the Shafi'i school. Which is a welcome contribution, but by no means a "final word" about these rulings, for each of the four schools has a large literature of hadith evidences, and not just the Shafi'i school reflected by Sabiqs work. The Maliki school has the Mudawwana of Imam Malik, for example, and the Hanafi school has the Sharh ma'ani al-athar [Explanation of meanings of hadith] and Sharh mushkil al-athar [Explanation of problematic hadiths], both by the great hadith Imam Abu Jafar al-Tahawi, the latter work of which has recently been published in sixteen volumes by Mu'assasa al-Risala in Beirut. Whoever has not read these and does not know what is in them is condemned to be ignorant of the hadith evidence for a great many Hanafi positions.
What I am trying to say is that there is a large fictional element involved when someone comes to the Muslims and says, "No one has understood Islam properly except the Prophet (Allah bless him and give him peace) and early Muslims, and our sheikh". This is not valid, for the enduring works of first-rank Imams of hadith, jurisprudence, Qur'anic exegesis, and other shari'a disciplines impose upon Muslims the obligation to know and understand their work, in the same way that serious comprehension of any other scholarly field obliges one to have studied the works of its major scholars who have dealt with its issues and solved its questions. Without such study, one is doomed to repeat mistakes already made and rebutted in the past.
Most of us have acquaintances among this Umma who hardly acknowledge another scholar on the face of the earth besides the Imam of their madhhab, the Sheikh of their Islam, or some contemporary scholar or other. And this sort of enthusiasm is understandable, even acceptable (at a human level) in a non-scholar. But only to the degree that it does not become taassub or bigotry, meaning that one believes one may put down Muslims who follow other qualified scholars. At that point it is haram, because it is part of the sectarianism (tafarruq) among Muslims that Islam condemns.
When one gains Islamic knowledge and puts fiction aside, one sees that superlatives about particular scholars such as "the greatest" are untenable; that each of the four schools of classical Islamic jurisprudence has had many many luminaries. To imagine that all preceding scholarship should be evaluated in terms of this or that "Great Reformer" is to ready oneself for a big letdown, because intellectually it cannot be supported. I remember once hearing a law student at the University of Chicago say: "I'm not saying that Chicago has everything. Its just that no place else has anything." Nothing justifies transposing this kind of attitude onto our scholarly resources in Islam, whether it is called "Islamic Movement", "Salafism", or something else, and the sooner we leave it behind, the better it will be for our Islamic scholarship, our sense of reality, and for our din.