This one-post blog is an essay on the Sefer Yetzirah, a proto-Kabbalist Jewish work compiled sometime before 900 c.e. It relies primarily on the earliest known commentary and publication of that work, by Saadia in the tenth century, to examine the relationship of the first four sefirot named in the first chapter to the six that follow, and of the "mother letters" to the "doubles" and "simples" as characterized in that text. In particular, it questions whether the mother letters correspond to the three dimensions of space. The essay is divided into seven sections, followed by their footnotes and then four appendixes, A to D, giving more extensive selections from Saadia, my translation from Meyer Lambert's French translation of Saadia, of which his French is given in the Appendices' footnotes : 1. Case and Saadia on the Cube of Space 2. Saadia in the context of his time. 3. The distinction between Sefirot and directions. 4. What sefir