Benefic and malefic grahas: what the terms mean
In the classical scheme grahas are called benefic (shubha) or malefic (krura). The labels describe their general effect in the standard reading, and they are not moral judgements.
What it is
Jupiter and Venus are natural benefics. The waxing Moon and Mercury, when with benefics, are benefic too. The Sun, Mars, Saturn, Rahu and Ketu are natural malefics. Waning Moon is weakly malefic in some texts.
How it is worked out or read
A graha's benefic or malefic character can be changed by its house, its lordship and its dignity, which is why the same graha is read differently in different charts.
Where it appears on this site
The labels are used in the yoga article, where several yogas depend on benefics. This site does not give a benefic score.
Natural benefics and malefics
The classical texts divide the grahas into natural benefics, shubha grahas, and natural malefics, papa grahas. Jupiter and Venus are the natural benefics. The Moon is benefic when waxing and bright, and less so when waning and dark. Mercury is benefic when alone or with benefics, and takes on a malefic character with malefics. Saturn, Mars, Rahu and Ketu are the natural malefics, and the Sun is usually counted as a mild malefic. These labels describe the general nature of each graha.
Functional roles by Lagna
A second classification depends on the houses each graha rules for a given Lagna. Lords of trikonas, the first, fifth and ninth, are considered functional benefics. Lords of the third, sixth and eleventh are considered functional malefics. Lords of kendras are neutral in themselves, and the eighth lord is generally treated with caution. So the same graha can be a natural malefic but a functional benefic in one chart, or a natural benefic but a functional malefic in another.
Yogakarakas
A graha that rules both a kendra and a trikona for a given Lagna is called a yogakaraka and is considered especially favourable. Saturn is the yogakaraka for Vrishabha and Tula Lagnas, ruling the ninth and tenth for Vrishabha and the fourth and fifth for Tula. Mars is the yogakaraka for Karka and Simha Lagnas. Venus is the yogakaraka for Makara and Kumbha Lagnas. These cases show clearly how a natural malefic can become the most helpful planet in a chart.
Kendradhipati dosha
A related rule says that natural benefics lose some of their beneficence when they rule kendras, a condition called kendradhipati dosha. Jupiter ruling the seventh and tenth for a Mithuna Lagna is a standard example. The rule is applied with varying emphasis by different authorities, and it is a good reminder that a planet's nature and its role in a particular chart must be read together.
Using the labels well
Benefic and malefic are technical terms, not moral judgements. A malefic placed well can give discipline, courage and endurance; a benefic placed badly can give excess or complacency. A careful reading weighs the natural nature, the functional role, the dignity and the house before deciding how a graha is likely to act in a given chart.