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Finding the moment of conception : The Rule of Petosiris (Málaga 18-21 February 2015)

Dear pioneers, fellow students and enthusiasts in the study of Ancient

Astrology,

Conception horoscopy is far from being a favourite subject in the study

of astrology. The thesis by Kathrin FROMMHOLD, published 10 years ago, must

be considered a remarkable and (by the way: well-known) exception as it is to

THIS day the only exhaustive scientific analysis on conception horoscopy – a

study to which I am deeply indebted.

In scientific literature you may read that in ancient astrology there had

been quite a debate about the correct beginning in order to cast precise

horoscopes and especially nativities AND that the idea was finally abandoned

due to its speculative nature or poor results.

At least this is identical to what we read in Ptolemy’s third book on

individual horoscopy, a discipline of astrology he calls genos genethliakon or

“genethlialogy” which in modern terminology is often limited to natal

astrology.

// Slide 1 //

Nevertheless his understanding of conception and birth as two

distinct, but celestially linked beginnings of human life may help us for our

own investigation. In the following, I would like to point out three

observations Ptolemy makes in his chapter peri sporas kai ektropes (On

conception and birth):

(1)

Ptolemy distinguishes between two beginnings of human life:

The first and natural beginning (arche) is the moment of conception. In

this moment the main characteristics (idiomata) of every human being are

determined.

Birth as the second beginning (katarche) comes along with the

development of these characteristics and one’s individual capabilities,

embracing the whole set of bodily and mental faculties.

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(2)

If the moment of conception is known, its reliability as an indicator for

physical and psychological characteristics outperforms the indicating quality

of birth. With the help of a conception horoscope, it is even possible to

predict the prenatal and intrauterine development of the foetus.

The moment of conception may be known by chance (symptomatikos)

or by active monitoring (parateretikos) which reminds us of natural family

planning of our times. Both require direct or indirect knowledge of the

moment of conception, none of them tries to find out by calculating

backwards.

At this point, Ptolemy treats the second option, i.e. the moment of

conception is unknown, almost as an afterthought: He states that a

determination ex post involves too many uncertainties or is even completely

impossible. We read the same argument in Sextus Empiricus and Hippocrates.

The astrologer is hence obliged to turn to the second beginning (katarche), to

birth instead of conception, since in most cases the moment of conception

remains unknown.

(3)

The semen as the basic matter of procreation is directly influenced by

the celestial constellation; the nature of a human being is therefore

determined at his natural beginning.

Still: the birth constellation plays a crucial role as it triggers birth

itself(!).Nature stimulates birth once the constellation resembles the one in

which conception took place. This is also the reason why an astrologer may

resort to the birth constellation for it basically shows the same thing and –

according to Ptolemy – is even more complete as it includes the

characteristics (hence called: symptomata) post-partum: when the newborn

has left the mother’s womb.

In short, while emphasising the importance of conception for its

indicating quality, Ptolemy circumvents the tricky part of the problem by

postulating an analogy between the celestial constellations at both moments

in order to focus on birth alone.

// Slide 2 //

There is another astrological tradition in Antiquity which was less

cautious in dealing with conception as a basis for genethlialogy. They insisted

on a 3rd alternative to obtain the moment of conception: by calculation. All

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methods of calculation are based upon the assumption made by Ptolemy that

the two constellations do resemble. But before shedding light on the most

prominent computing method, the so-called ‘Rule of Petosiris’, let’s examine

the earliest known example of a conception horoscope.

// Slide 3 //

Ancient Astrologers felt quite early the need to make conception, not

birth the actual starting point for casting individual horoscopes. While

conception may already have played an important role in Babylonian

divination, first sound evidence dates back as early as 257 BC, preserved in a

two-sided Seleucid horoscope which by modern scholars is generally

identified as the first conception horoscope.

// Slide 4 //

The cuneiform tablet shows on its observe the 17th of March ─ on its

reverse the 15th of December of the very same year. The interval between

the two dates being 273 days or ten sidereal months: the exact time span that

in ancient astrology was considered the normal length of pregnancy.

From an additional testimony given by Vitruvius, we may infer that the

beginnings of such practice can be traced back to a time when Babylonian-

Chaldean divination and Greek science started to merge.

Vitruvius reports that Achinapolus, one otherwise unknown successor

of the much-admired priest of Bel Marduk and important intermediary for

astrological knowledge Berosos, developed rules in genethlialogy based upon

conception instead of birth.

// Slide 5 //

One of the most important places for these astrological and scientific

ideas to meet was the Egyptian mega-city and cultural melting pot Alexandria.

Here, the practice of casting conception horoscopes was very much alive in

the first century BC, if we believe what is attested by the fervent critic Philo of

Alexandria.

It is therefore not surprising to find the most influential theory on conception

attributed to the legendary figure Petosiris. In the past there have been

several attempts to identify Petosiris with a certain priest from the late 4th

century BC. Since the discovery of a demotic papyrus, we tend to believe that

Petosiris’ original name was Petesis who is said to have offered his astrological

work to king Nechepso, identified with Necho II of the Late Period. The

‘Astrologoumena’, the work which is generally ascribed to – BOTH – Petosiris

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and Nechepso, must have become a true bestseller. At least, this is what we

can tell from the frequency Greek and Roman astrologers are giving credit to

it. Not to speak of the far superior number of times when they did not specify

their source. Literary evidence of this first cherished ‘bible of astrology’ – long

before Ptolemy’s Tetrabiblos ─ remains however a complex puzzle to be

solved as its fragments are widely scattered.

First comprehensive accounts of the Rule of Petosiris, which – of the

four known methods for computing conception horoscopes – was

undoubtedly the most influential one, appear much later in the 2nd century

CE.

// Slide 6 //

Whereas the name ‘Rule of Petosiris’ given by FROMMHOLD, who in her

thorough study reassembles all material dealing with conception horoscopy,

may suggest that the rule was unanimously attributed to these legendary

figure, it should not go unmentioned that in ancient sources we feel a higher

degree of uncertainty concerning its origin:

Vettius Valens, our earliest source, cites the rule several times

throughout his unsystematic work without giving away any information on its

provenance whereas in other contexts he does cite from Petosiris.

Porphyry, who relies heavily on Antiochus of Athens and seems to

have copied the relevant paragraphs from his Eisagogika, does not only cite

the rule in its complete form but is the first in chronological order who

ascribes it to Petosiris.

Hephaistion and Proklos both are more ambiguous in referring to the

“old Egyptians around Petosiris”, describing a somehow master-disciple

relationship.

At least there appears to be a consensus that the calculation method

stems from an Egyptian/Alexandrian school that preserves the doctrine of its

famous teacher and revered founder. By mentioning Petosiris and Zarathustra

in the same breath, thus naming two founding fathers, Proklos obviously

underlines the age and significance of the rule. Petosiris for astrology on the

one hand (=Egyptian tradition), Zarathustra on the other for divination and

magic (=Babylonian tradition).

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// Slide 7 //

Without doubt, Porphyry provides us with the best information to

understand the rule.

Based upon the belief that the constellations at the moment of

conception and birth are inextricably linked, the ‘Rule of Petosiris’ establishes

an interdependency between the position of the moon and the ascendant at

these two precise moments.

The first part of the formula asserts that the zodiacal sign in which the

moon resides at the moment of conception is the same sign that ascends at

birth. The second part states analogously: the zodiacal sign in which the moon

resides at birth is the same sign that ascends at the moment of conception.

// Slide 8 //

We may illustrate the rule with the help of a graphic depiction in two

horoscopes, the one on the left for conception, the one on the right for birth.

Respective starting point is the position of the moon. When the moon is in

Aquarius in the moment of conception, the ascendant at birth must reside in

the very same sign. When the moon’s position at birth is libra, the ascending

sign in the moment of conception was libra as well.

***When born at night, the position of the ascendant might as well be

in opposition to the moon (only Porphyry)***

// Slide 9//

Although the rule as formulated by Porphyry suggests that his main

interest is to determine the zodiacal position of the ascendant at birth and

conception, the title given to the paragraph indicates that he wants to

ascertain the position of the moon in conception. Without stating this

explicitly, the first formula may as well serve the other way round: With the

knowledge of the ascendant in the moment of birth, it is also possible to

determine the position of the moon at conception.

Let’s have a look on the varying purposes for ancient astrologers to

quote the rule of Petosiris.

// Slide 10 //

Antiochus of Athens uses the rule in the context of his own lunar

method, which seems to focus only on the computation of the moon in the

moment of conception. The remaining fragments are hard to understand and

his technique is based on a quite obscure sequence of calendar calculations.

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Hephaistion, who comments on this approach, criticises its obvious

lack of clarity but includes it anyway in his inventory of computation methods

for the sake of completeness.

Hephaistion himself presents the most versatile use of the formula. In

his second book Hephaistion only differs from Porphyry in changing the order

of the two parts of the formula. From this modification and his following

statements which highlight the possibility to use the formula for the

subsequent correction of the birth ascendant, the overall focus is laid upon

the computation of the ascendant.

Here, we might grasp the original purpose of the formula as the

computation of the ascendant – the most important point of reference in

Hellenistic astrology – which was especially difficult in Antiquity due to a lack

of accurate tools for observation and time measurement.

But then again, Hephaistion quotes the formula in a totally different

context. In his third book he gives advice on the ideal moment for sexual

intercourse in marriage. By scheduling conception on a certain date with

regard to the position of the moon and the ascendant, it is possible to achieve

a favourable birth constellation. ***i.e. a katarchic use of the formula***

Our earliest source, Vettius Valens cites the rule in all possible ways in

three different passages of his work. Two times he even claims accuracy

within one degree. In addition to that, his use of vocabulary is striking. He

employs short forms of the words ‘ascendant’ and ‘zodiac’ (hora instead of

horoskopos; zoon instead of zodion) as in poetic language. We like to believe

that he echoes the work of Petosiris-Nechepso in compliance with some of

the preserved fragments composed in Greek verse. Whereas Valens makes

the first reference to the Rule of Petosiris in a chapter which deals with the

length of pregnancy, the other references are made in connection with the

prediction of one’s lifetime.

// Slide 11 //

Proklos uses the rule in the same way Hephaistion does. After stating

the standard formula he claims that its inversion must be valid as well, more

confusing is his later comment that Ptolemy approved of the rule. In early

research, this enigmatic sentence was often (mis)understood as an evidence

for interpreting the Pseudo-Ptolemaic Karpos, widely known under its latin

name Centiloquium, as an ancient work.

Indeed, we do find the ‘Rule of Petosiris’ in its standard version in the

Centiloquium but there is no mention of the text by ancient astrologers. All

evidence points to a certain Ahmad Ibn Yusuf or latinised Hametus, an arab

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mathematician who died in 912 AD, who did not only comment on the

compendium but actually is very likely to have composed it himself under the

name of Ptolemaios. It is from the Karpos that the ‘Rule of Petosiris’, now

ascribed to Ptolemy and Hermes, made its way to the astrological manuals of

the Middle Ages and the Renaissance. Known under the name Trutina

Hermetis ***itself derived from a mislecture***, it was mainly used to correct

the birth ascendant as proposed by Hephaistion.

The ‘Rule of Petosiris’ is one of four ancient methods for computing

conception horoscopes, but while its reception may be easily assessed, its

significance in practical use for all Greco-Roman antiquity must remain

uncertain. Besides some example charts given by Vettius Valens and

Hephaistion, we have no Greek or Roman testimonies of conception

horoscopes.

TODAY the computation of the moment of conception still plays an

important role in gynaecology and obstetrics and is not only used to

determine the ‘due day’ but also to estimate the exact gestational age of the

foetus and more importantly its viability.

Instruments of choice are ‘Naegele’s rule’ (1812) or a so-called

gravidarium:

// Slide 12 //

The basic principle of the latter is still very similar to what ancient

astrology did with the help of the zodiac:

Reading a counter-clockwise time machine.

Thank you for your attention!

ca. 18-20min.

Finding a Moment of Conception : The rule of Petosiris Congreso Internacional Ad astra per corpora - Astrología y sexualidad en el mundo antiguo

Christoph L. Hesse; Student (M1) at the Centre for the History and Culture of the Eastern Mediterranean (GKM), Münster

Málaga, del 19 al 21 de febrero de 2015

Ptolemy’s observations on conception & birth (Ptol. apotel. 3,2,1-4.7)

• Ptolemy distinguishes between two beginnings of human life:

First natural beginning (ἀρχή): determination of human characteristics (ἰδιώματα)= conception

Second beginning (καταρχή): development of human capabilities (συμπτώματα) = birth

• If moment of conception is known : (known by chance συμπτωματικῶς or by monitoring παρατηρητικῶς)

Better indicator than birth Helps even to predict prenatal/intrauterine development of the fetus

However, in most cases moment of conception remains unknown. → the astrologer is forced to focus on birth (καταρχή) for casting horoscopes !

• Nature stimulates birth when :

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Constellation (at birth) ≈ Constellation at conception

Finding the moment of conception

• Moment of conception may be known (cf. Ptol. apotel. 3,2,1-4.7) :

by chance συμπτωματικῶς [1]

by monitoring παρατηρητικῶς [2]

by calculation μεθοδικῶς (cf. Heph. 2,1,35) [3]

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Constellation (at birth) ≈ Constellation at conception

↓

Constellation (at birth) → Constellation at conception

↓

calculating backwards to

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First evidence for conception horoscopy – BM33667

(ROCHBERG 1998: 73f.)

(S.E.) 53 = Mar 17 (257 BC)

(S.E.) 54 = Dec 15 (257 BC)

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A Seleucid horoscope – First evidence for conception horoscopy

rev. Dec 15 (257 BC)

obv. Mar 17 (257 BC)

273 Days ≈ 273 13 = 10 sidereal months

The ‘Rule of Petosiris’

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The ‘Rule of Petosiris’

Ancient Author (siglum acc. ThLL) attributes to (passage)

Vettius Valens (Val.) Ø

Antiochus of Athens (Ant. epit. 1, ex Eisag.)

Ø [*Πετόσιρίς (?), cf. Porphyry]

Porphyry (Porph. Eisag.) ὁ δὲ Πετόσιρίς (38b)

Hephaistion (Heph.) οἱ δὲ παλαιοι Αἰγύπτιοι οἱ περι Πετόσιριν (2,1,2) δὲ οἱ περὶ Πετόσιριν (3,10,5)

Proklos (Prokl. In remp.) οἱ δὲ περὶ Πετόσειριν Αἰγύπτιοι καὶ Ζωροάστρης (2,37)

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Understanding the ‘Rule of Petosiris‘

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The complete formula according to Porphyry (Porph. Eisag. 38b):

• Interdependency between the position of the moon (MN/ ☽) and the ascendant (ASC)

at the two beginnings: conception (C) & birth (B)

• First part of the formula: The zodiacal sign in which the moon resides in the moment of conception is the same sign that ascends at birth. • Second part of the formula: The zodiacal sign in which the moon resides at birth is the same sign that ascends in the moment of conception

(1) MN (C) → ASC (B)

(2) MN (B) → ASC (C)

The ‘Rule of Petosiris’: (1) MN (C) → ASC (B) (2) MN (B) → ASC (C)

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Ex. Left: Conception fc. Right: Birth

1 Moon (Aquarius) → Ascendant (Aquarius)

2 Ascendant (Libra) ← Moon (Libra)

The Inversion of the Rule of Petosiris: ASC (B) → MN (C)

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Ex. Left: Birth fc. Right: Conception

1inv Ascendant (Libra) → Moon (Libra)

The Use of the Formula

Ancient Author (siglum acc. ThLL)

uses formula main interest(s)

Vettius Valens (Val.) [*(1) MN (C) → ASC (B)] (2) °MN (B) → °ASC (C) (1inv) °ASC (B) → °MN (C) (2inv) ASC (C) → MN (B)

used in bigger contexts (Gestation period; Prediction of life-time)

Antiochus of Athens (Ant. epit. 1, ex Eisag.)

in context with own lunar method

[*Zodiacal position of the MN (C)]

Porphyry (Porph. Eisag.) (1) MN (C) → ASC (B) (2) MN (B) → ASC (C) (1inv) ASC (B) → MN (C)

Zodiacal position of the MN (C)

Hephaistion (Heph.) (1) MN (C) → ASC (B) (2) MN (B) → ASC (C)

Zodiacal position of the ASC (C); Correction of ASC (B); Sheduling a favorable birth constellation

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The Use of the Formula – Its Reception in the Middle Ages and the Renaissance

Ancient Author (siglum acc. ThLL)

uses formula main interest(s)

Proklos (Prokl. In remp.) (1) MN (C) → ASC (B) (1inv) ASC (B) → MN (C) (2inv) ASC (C) → MN (B)

Scheduling a favorable birth constellation

Ps.Ptol. Karpos 51 (lat. Fructus, Centiloquium; arab. Kitǡb Thamara)

(1) MN (C) → ASC (B) (2) MN (B) → ASC (C)

Zodiacal position of the ASC (C); Correction of ASC (B)

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Calculating conception and birth today – The Gravidarium

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