The number three was the most sacred number to the Celts. It is from them that comes concepts like 'The third times the charm,' and some say that the idea of the trinity even came from druids, many of whom were converted to christianity taking up priesthood and monkhood in the first few centuries of the common era. One of the oldest Celtic bardic documents speaks of something referred to as 'the three cauldrons' which are found within all of us.

 Please read this 7th century bardic work titled 'The Three Cauldron's of Poesy' for important background on the old celtic threefold mind concept discussed below.

The three cauldrons likely have to do with more than just poesy or intellect. These three cauldrons are like centers of the soul, almost like chakras except that there are only three. It might also be describing three different states of existence. It might be possible to fit many things into these three cauldrons.

For instance in ancient astrology, traced back to ancient greece and beyond there is found a very old concept of three qualities of mankind. Spirit, Soul, and manifestation. In astrology these correspond to the Sun, the Moon, and The ascendant / midheaven. This is a little bit different and more meaningful than modern pop astrology where the sun is ego, the moon is emotions, and the ascendant (or rising sign) is outward appearance. And yet, these modern interpretations are still applicable here.

Much good recent work has been done in recovering the lots bits of ancient astrology. Check out these sites for more information.
The History of Astology (article by Rob Hand)
Archives for the Retrieval of Historical Astrological Texts (http://robhand.com )
J. Lee Lehman, Ph.D (http://www.leelehman.com/ )
Project Hindsight (http://www.projecthindsight-tghp.com )

Now adays the Sun is quite elevated in importance in astrology. But in ancient times the moon and rising sign were just as important, in some cultures the Moon or Rising sign were even more important than the sun.

This system of threefold correspondences below is not represented as an authentic ancient celtic system. It is a synthesis of old celtic ideas, old astrology, some other indo-european ideas, and a few modern concepts.

Pliny wrote that the Druids were quite familiar with Greek natural philosophy (which includes astrology and these concepts of spirt, soul, and manifestation) and that they appreciated it and that their own beliefs were quite similar and compatible. The roots of astrology go back quite far, to prebabylonian times, and every culture in europe has a system of astrology that is fairly similar. This includes the so called Vedic astrology that is based on ancient Vedic, Greco Roman, and modern Hindu thought.

Therefore it is reasonable to assume that the Celtic / Druidical system of astrology would be somewhat vaugely similar to what we use today, with some important differences that can only be speculated at. For instance, the idea of houses is fairly modern, coming probably from late Rome or Egypt. However, knowledge of the points of the Ascendant (or rising sign) and the Midheaven (or zenith) are quite ancient indeed.

Here follows an attempt to fuse these threefold ideas of mind, spirit, karma, and astrology into one workable whole, which while it may not be something precisely resembling what druids of old may have used, they most certainly would have understood it and probably appreciated it.