century; however, sola gratia and sola fide were used in phrases by the Reformers themselves. In 1554, for example, Philip Melanchthon wrote, "sola gratia justificamus et sola fide justificamur" ("only by grace do we justify and only by faith are we justified"). All of the solae appear in writings by the Protestant Reformers, but they are not catalogued together by any.

In 1916, Lutheran scholar Theodore Engelder published an article titled "The Three Principles