Sutras / S-001
Sign exchange: either planet's period activates both
The rule
When two planets occupy each other's signs (परिवर्तन योग, parivartana yoga), each behaves as though it sits in its own sign. During the dasha or antardasha of either planet, the houses ruled by both planets are activated together.
Classical basis
Phaladeepika classifies sign exchanges into three kinds by the houses involved: maha (between auspicious houses), dainya (involving the 6th, 8th or 12th) and khala (involving the 3rd).verse ref. being checked Laghu Parashari sets out that a dasha delivers the results of the houses its planet rules and the planets it is linked with.verse ref. being checked The timing statement above combines the two; it is a working hypothesis derived from them, not a verse in its own right.
Test case: Chart A
Gemini ascendant. Mercury rules the 1st and 4th houses and sits in the 8th, in Saturn's sign Capricorn. Saturn rules the 8th and 9th and sits in the 4th, in Mercury's sign Virgo.
Because the exchange involves the 8th house, Phaladeepika would class it as dainya. It also links the ascendant lord with the 9th lord, which is why it was expected to deliver events tied to home (4th) and to fortune and long journeys (9th).
Chart shared with the owner's consent and anonymised.
Events tested
| Period | Dates | Expected | What happened | Stated in advance? | Result |
|---|---|---|---|---|---|
| Jupiter–Mercury | May 2013 – Sep 2015 | Long journey, change in fortune (9th via exchange) | Moved abroad, Jan 2014; career step up | No · found during review | Supporting |
| Jupiter–Venus | Aug 2016 – Apr 2019 | Property: Venus sits with the 4th lord | Bought and moved into a home, Oct 2016 | Yes | Hit |
| Saturn–Saturn–Mercury | Mar 2025 – Aug 2025 | Home change: Saturn in the 4th, Mercury the 4th lord | Purchase completed Jun 2025; moved in Aug 2025 | Yes | Hit |
How much does this show? Each pre-stated window covered roughly 40% of its year, so both landing by chance alone has odds of very roughly one in six. That is encouraging for one chart and proves nothing on its own. The rule moves to Supported only after it holds across at least 30 charts.
Supporting sutras on the same chart
Two general sutras were tested on Chart A and did not hold on their own: S-003 (Moon in the 12th brings relocation in its antardasha) and S-004 (Rahu in the ascendant turns life towards foreign lands or technology). Both apply a planet's usual meaning without regard to the chart's structure. The contrast with S-001 is the most useful finding so far.
Next tests
The same chart enters Saturn–Mercury from October 2027, the first period in which both exchanging planets run together. Under this rule, that window should carry the strongest combined results for the 1st, 4th, 8th and 9th houses. The outcome will be recorded here.