Who first came up with the "four attributes of Scripture"?

It looks like the "4 attributes" was first used by the theologian Wayne Grudem while the SCAN acronym itself was first used by Justin Taylor. The rest of this answer will provide evidence.

Another acrostic is NAPS which I found here (Mar 7, 2012), but expresses the same attributes, substituting "Clarity" with "Perspicuous" (a more historic term). Yet another is SNAC described here, which is another ordering of the same 4 attributes.

Justin Taylor's blog article

Justin Taylor wrote the blog article "SCAN the Scriptures" on Aug 11, 2010, which begins as follows:

If you want a quick and easy way to memorize the traditional four attributes of Scripture, just put them in the order of S.C.A.N.:

• the Sufficiency of Scripture
• the Clarity of Scripture
• the Authority of Scripture, and
• the Necessity of Scripture

5 days later, another blogger wrote a short post "Sola Scriptura and SCAN!" dated Aug 16, 2010, which links to the article above, saying:

Justin Taylor gave a handy way for us to remember the key attributes of Scripture– just put them in the order of S.C.A.N.:

• the Sufficiency of Scripture
• the Clarity of Scripture
• the Authority of Scripture, and
• the Necessity of Scripture Read the rest of the post for a helpful explanation of what each one of these characteristic mean. It’s really worth your time.

But where did Justin Taylor get the idea of the "four attributes" from?

Timothy Ward's book

A clue is from a book he referenced: Words of Life: Scripture as the living and active word of God by Timothy Ward published by IVP only 1.5 years earlier on Feb 22, 2009. Chapter 4 of that book is titled The Attributes of Scripture: A Doctrinal Outline which contains the following sections:

• The necessity of Scripture
• The sufficiency of Scripture
• The clarity of Scripture
• The authority of Scripture

Skimming the book itself I couldn't find the acronym S.C.A.N., so Tim Ward didn't come up with it himself. At any rate, the section title order doesn't match S.C.A.N.

Wayne Grudem's book

Going back in time to 1994 we find some similarity in the table of contents of Wayne Grudem's very popular book Systematic Theology: An Introduction to Biblical Doctrine:

• Chapter 4: The Four Characteristics of Scripture: (1) Authority
• Chapter 6: The Four Characteristics of Scripture: (2) Clarity
• Chapter 7: The Four Characteristics of Scripture: (3) Necessity
• Chapter 8: The Four Characteristics of Scripture: (4) Sufficiency

I also cannot find the S.C.A.N. acronym in the book, so Wayne Grudem didn't come up with it either. The chapter order also didn't match.

Luther's understanding of sola scriptura

A 1960 Concordia Theological Monthly journal article Luther's Sola Scriptura by a historian Lewis W. Spitz (d. 1999), specializing in Reformation who also wrote the well cited 1984 book The Protestant Reformation: 1517-1559 traced the development of Martin Luther's own understanding of Sola Scriptura.

Quote from the journal article (emphasis mine):

Luther's sola Scriptura implies the divine authority, efficacy, perfection or sufficiency, and perspicuity of Holy Scripture, but above all Christ as the center of it all. For Luther there is no sola Scriptura without solus Christus. Werner Elert shows that for Luther the divine properties of Scripture are based on the fact that for him the Bible is Christocentric.

So three of the "four attributes" (authority, sufficiency, perspicuity) came from Luther himself. The "four attributes" adds "necessity" but drops "efficacy".

Wikipedia article

In the Lutheran section of the the Wikipedia article Sola Scriptura referencing pages 27-29 from the 1934 book Popular Symbolics: The Doctrines of the Churches of Christendom and of Other Religious Bodies Examined in the Light of Scripture published by a Lutheran publisher Concordia Publishing House, the author spells out Lutheran Sola Scriptura in terms of "inspiration, authority, clarity, efficacy, and sufficiency".

The "four attributes" drops "efficacy" and "inspiration" but adds "necessity".

Westminster Confession of Faith

Westminster Confession of Faith (1647) begins with the Necessity of Scripture in Chapter 1 (Of the Holy Scripture), Section 1:

Although the light of nature, and the works of creation and providence do so far manifest the goodness, wisdom, and power of God, as to leave men inexcusable; yet are they not sufficient to give that knowledge of God, and of His will, which is necessary unto salvation: therefore it pleased the Lord, at sundry times, and in divers manners, to reveal Himself, and to declare that His will unto His Church; and afterwards, for the better preserving and propagating of the truth, and for the more sure establishment and comfort of the Church against the corruption of the flesh, and the malice of Satan and of the world, to commit the same wholly unto writing; which maketh the Holy Scripture to be most necessary; those former ways of God's revealing His will unto His people being now ceased.

How Wayne Grudem reorganized the historic characteristics in his book

Wayne Grudem understandably makes explicit this very important "necessity" attribute, which in other systematic theologies are discussed more or less implicitly. Looking closer at Wayne Grudem's Systematic Theology book, I can see that he covers "inspiration" under chapter 4 (authority). He also covers "efficacy" as Point #1 (Teaching of the Word) along with 10 other means of grace in Chapter 48 (Means of Grace Within the Church).

Conclusion

Comparing Wayne Grudem's "4 attributes" with other list of terms related with sola scriptura we can see how Wayne Grudem came up with his own organization of the characteristics / attributes of Scripture in his Systematic Theology book. Since Wayne Grudem's book is a very popular systematic theology book among evangelicals which has been around since 1994, I think it is safe to say that the 4 attributes mentioned in a variety of blog articles we encounter post 1994 originated from the theologian Wayne Grudem. Validating my thesis, I also couldn't find any match when skimming Google search dated before 1994 using the keywords: "scripture" "authority" "clarity" "necessity" "sufficiency".

As for the S.C.A.N. acronym, it's very likely that Justin Taylor came up with it after reading both books and noticing Chapter 4 section titles of Timothy Ward's book and Table of Contents of Wayne Grudem's book! We don't know for sure of course, but I think there is enough circumstantial evidence to say that Justin Taylor was the inventor since Google search also didn't yield any reference to that acronym before Justin's blog article (Aug 11, 2010).