High quality terminologies are a fundamental requirement in a range of health care applications. To ensure high quality terminologies we should reflect about the understandability, reproducibility and utility criteria within a terminology. This paper describes efforts to improve the understandability of SNOMED. We describe the problem related to the grammatical conjunctions "and" and "or" and how we applied basic semantic rules defined by the SNOMED Editorial Board. The results show that the meaning of "and" and "or" in SNOMED can be made explicit in almost all cases and can be done in a reasonable, reliable, and reproducible manner.