Prediction is the chief objective of Predictive Astrology. A learned astrologer has to make study of the three different parts of a horoscope - 1.Yoga, the combination of planets and Lords, 2. Period-sub-period i.e. Dasha, 3. Gochar that is, transit. All the three parts are the supplements of each other. Yoga is the most important among all the three parts. Period-sub-period i.e. dasha may prove to be futile if there is no Yoga in a horoscope. For example, Period-sub-period cannot bless a native with a child if there is no Santan Yoga in his horoscope. Dasha might be of Lord of fifth house or of Karaka planet.