Here's what they used:
* Quipus: These were knotted strings of different colors and lengths, with the knots and their positions representing numerical and other data. They were used for accounting, census records, and historical narratives. While they had a high degree of complexity, they were not a full written language capable of expressing the full range of human thought.
* Symbols: The Inca used pictographs and ideograms on ceramic pottery, textiles, and other objects to depict events, people, and concepts. These were not a complete writing system but served as visual reminders and records.
* Oral traditions: The Inca relied heavily on oral storytelling and the memory of their elite to preserve history, laws, and knowledge.
Why the Inca didn't develop a phonetic writing system is a matter of debate:
* Possible lack of need: Their complex quipus and oral traditions may have been sufficient for their needs.
* Limited materials: The Inca lacked writing materials like paper or papyrus.
* Cultural factors: Their worldview may have emphasized visual communication over written language.
In summary, the Inca society possessed sophisticated methods of record-keeping and communication, but they did not develop a written language with a phonetic alphabet like we know it.