When a yoga is weak or cancelled
A yoga's strength depends on the strength of the grahas involved, the houses, the aspects, and whether a cancellation (bhanga) applies. The classical texts state these conditions in detail.
What it is
Cancellation rules say a yoga or a weakness can be cancelled by a stated condition, such as a strong lord in a kendra. These rules are numerous and their lists vary between schools.
How it is worked out or read
The site checks the nine standard yogas for presence only. It does not compute strength or apply cancellation, and each result is marked as presence by the rule.
Where it appears on this site
The nine checked yogas are in the birth chart. The caution article explains how to use the result.
A yoga is only as strong as its planets
Classical texts repeatedly say that a yoga gives its full results only when the planets forming it are strong. Strength is judged in several ways: dignity, meaning whether the planet is exalted, in its own sign, in a friend's sign, or debilitated; house position, with kendras and trikonas favourable and the sixth, eighth and twelfth houses weakening; freedom from combustion near the Sun; and freedom from affliction by malefics. A Raja yoga formed by a debilitated, combust planet in the eighth house is very different from one formed by an exalted planet in a kendra.
Formal measures of strength
The Parashari system offers formal measures. Shadbala, the six-fold strength, combines positional, directional, temporal, motional, natural and aspectual strength into a single figure for each planet. Vimshopaka bala measures strength across the divisional charts. And the avasthas, or states, such as the age-like states from infant to dead based on degree, add further nuance. Not every reader uses all of these, but their existence shows how seriously the tradition took the question of strength.
Cancellation conditions
Many yogas come with specific cancellation rules. Kemadruma, the yoga of an isolated Moon, is cancelled in the texts by planets in kendras from the Lagna or the Moon, among other conditions. Neecha bhanga, the cancellation of debilitation, is itself a set of conditions that turn a debilitated planet's weakness into strength. Some Raja yogas are said not to work when their planets are in planetary war or are conjunct the lords of difficult houses. A reading that names a yoga without checking its cancellations is incomplete.
Timing: when a yoga acts
Even a strong yoga is said to show its results mainly during the dasha or antardasha of the planets involved, or when transits activate them. A person may carry a yoga in the chart for decades before its planets' periods arrive. This is why readers look at the dasha sequence alongside the list of yogas: it shows not only what the chart promises but when.
On this site
The yoga check on the birth chart page tests nine standard rules as written and says plainly that it does not apply cancellations or strength. That is deliberate: it shows whether the basic condition is met and leaves the weighing to the reader. These articles explain the strength and cancellation rules so that a reader can do that weighing with care.