---
type: "fhirpath-function"
title: "FHIRPath Function: not"
function: "not"
category: "Boolean Logic"
section: "6.5.3"
source: "fhirpath/functions.json"
---
# FHIRPath Function: not
Returns `true` if the input collection evaluates to `false`, and `false` if it evaluates to `true`. Otherwise, the result is empty (`{ }`):

|not |
|-|
|**true** |`false` |
|**false** |`true` |
|**empty** |empty (`{ }`) |
{:.grid}
## Summary
- **Category**: Boolean Logic
- **Section**: `6.5.3`
- **Return Type**: `Boolean`
- **Empty Input Result**: `empty`
- **Errors on Multiple Input**: `false`
## Description
Returns true if the input collection evaluates to false, and false if it evaluates to true. Otherwise, the result is empty.
## Arguments
- none
## Type Mapping
- n/a
## Example
```fhirpath
Patient.active.not() // true if patient is not active
```