40 is the Attic Greek numeral for the letter mu (μ), corresponding to the value of 40 in isopsephy. In the Greek alphabetic numeration system developed by Miletus in the 6th century BCE, letters of the alphabet are assigned numeric values; mu, the 12th letter, holds the value 40.

Position on the Tree of Life

40 corresponds to the 23rd Path of the Tree of Life, the path that connects Binah (Understanding) to Chokmah (Wisdom). This path is attributed to the letter Samekh in the Hebrew alphabet and to the zodiacal sign Sagittarius. The number 40, therefore, functions as a numeric bridge between these two supernal sephiroth.

Historical context

In Hellenistic gematria, 40 holds enduring ritual significance through its appearance in both Jewish and Christian scriptures. The forty days of the Flood (Genesis 7:4), the forty years of Israelite wandering in the desert, Moses’ forty days on Sinai, and Christ’s forty days of temptation in the wilderness all echo the same Temple-period convention: 40 represents a complete cycle of probation, purification, or transition. The Pythagorean tradition associated forty with the number of days required for a major bodily change, such as the formation of a fetus or the purification of the mother post-partum—a belief systematized by Hippocrates. Plutarch (Isis and Osiris, §56) records that the Egyptian priests counted a 40-day period of mourning for Osiris, a practice that later influenced the Christian Lent. In theurgic Neoplatonism, the number 40 was linked to the Greek letter mu, whose name is derived from the Egyptian word for water (mw), reinforcing the numeric link to the forty days of rain in the Noah cycle.

In the table of Liber 777 at Step 23 (the 23rd Path), the numeral 40 is the assigned value in the 'Numeration of Greek Alphabet' column.