Indian and Western astrological traditions share a substantial technical inheritance from the ancient world. They diverged afterwards in ways that go well beyond terminology.
The shared inheritance is real
Contact between the Hellenistic world and South Asia transmitted a body of technique, and Sanskrit texts from that period contain recognisably Greek terminology.
Both traditions consequently use the same basic apparatus: twelve signs, planetary bodies, houses derived from the daily rotation, and relationships measured by angular distance.
Each tradition combined that material with existing local practice, and the resulting systems then developed independently of one another over many subsequent centuries.
The reference point of the zodiac differs
The Indian tradition generally measures the zodiac against the fixed stars, while the Western tradition generally measures it against the seasonal points.
Because these two frames drift apart slowly, the same birth moment is assigned different sign positions in the two systems, which is the difference readers notice first.
Both conventions have long-standing justifications within their traditions, and the choice reflects different views about what the divisions are anchored to.
Predictive method is the larger difference
The Indian tradition places substantial weight on planetary period systems that divide a life into successive intervals attributed to different bodies.
Western practice relies more heavily on other timing techniques, including the movement of current planetary positions measured against the positions held in the birth chart.
These produce differently shaped readings, with one emphasising sequential life periods and the other emphasising ongoing conditions and transitions.
The questions asked are not the same
Practice in the Indian tradition has long been consulted on marriage compatibility, the timing of undertakings and family matters, and it operates within a wider ritual context.
Western practice over the last century has developed a strong psychological orientation, with charts read as descriptions of character and internal dynamics.
The difference in typical questions shapes vocabulary, training and how a consultation is conducted, quite apart from any technical divergence.
Exchange has resumed
Practitioners now read across the traditions, and techniques from each have been adopted by people trained principally in the other, which reverses centuries of separate development.
Some combine elements deliberately while others regard the systems as internally coherent wholes that lose consistency when mixed.
The disagreement is itself informative, since it concerns whether these are two dialects of one practice or two distinct practices with a common ancestor.