> For the complete documentation index, see [llms.txt](https://docs.snomed.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.snomed.org/snomed-international-documents/snomed-ct-glossary/n/necessary-condition.md).

# necessary condition

## necessary condition

A characteristic that is always true of a concept.

#### Notes

* Some *necessary conditions* can be represented as defining relationships but other *necessary conditions* that can be represented as OWL axioms cannot be represented as *relationships*.
* The relationship file represents the inferred view of *necessary conditions* in that can be represented as *relationships*.

#### Example

* If you have a [71620000 | fracture of femur|](http://snomed.info/id/71620000) , the morphological abnormality [72704001 | fracture|](http://snomed.info/id/72704001) must be present. Therefore, [116676008 | morphology|](http://snomed.info/id/116676008) = [72704001 | fracture|](http://snomed.info/id/72704001) is a *necessary condition* of [71620000 | fracture of femur|](http://snomed.info/id/71620000) .

#### Change Notices

* Prior to July 2018, SNOMED CT represented all *necessary conditions* in the stated view as defining relationships in the stated relationship file.
* Changes introduced in the July 2018 release of the International Edition mean that in future *necessary conditions* \_\_ in the stated view will be represented as axioms in the OWL axiom reference set file.

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