In astrology the term major aspect is a designation that is used to refer to a class of aspects that consists of the conjunction, sextile, square, trine and opposition.
This designation is primarily used in modern astrology in order to distinguish between major aspects and the minor aspects. Major aspects are generally viewed as the more important or powerful types of aspects, whereas minor aspects are viewed as less powerful or less important.
Originally in the Hellenistic and Medieval astrological traditions the term aspect was only used to refer to the so-called major aspects, because the concept of minor aspects had not been introduced. Johannes Kepler’s introduction of new aspects such as the semi-sextile, quincunx, and sesquiquadrate in the 17th century led to a redefinition of the term aspect.
Some astrologers adopted Kepler’s new aspects, although they treated them as being in a separate category from the five classical aspects. The five classical aspects became the major aspects, and the rest were relegated to the general category of minor aspects.
The major aspects are also often referred to as the Ptolematic aspects, in reference to the fact that they are the only five aspects mentioned by the 2nd century astrologer Claudius Ptolemy. In this way the terms “major aspect” and “Ptolemaic aspect” are synonymous, and in many texts they are treated as interchangeable.