Testimony-Counting Rule (Abu 'Ali al-Khayyat)
Definition
Abu 'Ali al-Khayyat's testimony-counting rule is the graduated principle, given in the closing 'Caution that must be Observed in Judgments' of The Judgments of Nativities, for weighing how confidently a chart supports a judgment. A signification resting on a single testimony is commonplace — of routine, slight force; two testimonies make it stronger; three perfect it, but only if the lords or significators are themselves strong and unimpeded. It tells the astrologer how to aggregate several chart-factors into one confident verdict.
In Tradition
Arabic natal astrologers hold that no single chart-factor decides a matter on its own: a judgment grows in force as independent testimonies accumulate. Abu 'Ali ranks a signification's strength by the number of agreeing testimonies — one is slight, two stronger, three perfecting it, provided the significators are sound — and by placement, since significations in cadent houses and movable signs read weak while those in angles and fixed signs read strongest. When good and evil fall together, the stronger by dignities is preferred.
In Practice
When you judge any topic, do not rest on one indication. Gather the independent testimonies bearing on it — the relevant house and its lord, the natural significator, the pertinent lot and its lord, the triplicity lords, and the aspects reaching them — and count how many agree. A single testimony makes the judgment commonplace and tentative; two agreeing testimonies let you judge with more confidence; three perfect it, so you may judge firmly, but only after confirming that the lords carrying those testimonies are themselves strong and unimpeded. Weigh placement too: a testimony in an angle and a fixed sign is strongest, one in a succedent house and a common sign middling, one cadent and in a movable sign weak. When a favorable and an unfavorable signification fall together, compare them by their dignities and keep the stronger, setting the weaker aside; if the two are equal, discard both. Apply this to every chapter so your firm statements rest on converging evidence.
Historical Origin
The rule is the closing Caution ('A Caution that must be Observed in Judgments') of Abu 'Ali al-Khayyat's The Judgments of Nativities, the final chapter before the text's doxology, preserved in James H. Holden's translation (AFA, 1988). Abu 'Ali, a pupil of Masha'allah, transmits the early-Abbasid Baghdad-school discipline of evidence-weighted judgment; Holden's footnote calls it a cardinal principle of astrological interpretation.