Conjunction

A conjunction is the aspect of zero degrees: two bodies occupy the same degree of zodiacal longitude, the closest possible relationship between two points in a chart. Popular usage counts it as one of the five classical, or Ptolemaic, aspects, but the ancient doctrine itself was narrower. In the Tetrabiblos, Ptolemy set out four true schemata, sextile, square, trine and opposition, on the reasoning that an aspect requires two bodies able to behold one another across the circle, much as two eyes regard each other; bodies standing in the same degree do not look across a distance at all, so he treated their relation as a synodos, a joining or fusion, rather than as an aspect in the strict sense. He nonetheless discussed conjunction's effects at length, since two natures merged into one produced the most decisive combination of all, closer to two notes sounding as one than to two notes in harmonic relation.

Later astrologers, more interested in practical judgment than in Ptolemy's causal reasoning, folded the conjunction back into the aspect set as its strongest member, and it is in that inclusive, five-aspect form that the term is generally used today. The word aspect itself descends from the Latin aspectus, a looking or a glance, translating the Greek schema Ptolemy used for the configurations he did recognise, so the conjunction's exclusion from the strict scheme was in part a matter of that word fitting awkwardly: two bodies fused into one are not really looking at anything, they have simply become a single thing to look at.