> For the complete documentation index, see [llms.txt](https://ampersandtarski.gitbook.io/documentation/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://ampersandtarski.gitbook.io/documentation/the-language-ampersand/truth.md).

# Truth

An information system should represent the truth. So, as a designer you must know a thing or two about truth.

Let us introduce some language to talk about truth. Consider a fact "Joe Smith lives in New York." from an Ampersand perspective. In Ampersand, we can analyse this as follows:

* Let `Person` and `City` be [***concepts***](/documentation/the-language-ampersand/the-concept-statement.md)*\*\*\*\**
* Let `"Joe Smith"` be an [***atom***](/documentation/the-language-ampersand/atoms.md) of the concept `Person` and `"New York"` an atom of the concept `City`.
* Let us use the [***relation***](/documentation/the-language-ampersand/relations.md) `livesIn[Person*City]` to contain our fact.
* `livesIn` is the ***relation name*** and `[Person*City]` is the ***signature*** of this relation.
* `Person` is the ***source*** of this relation and `City` is the ***target***.
* If the pair `("Joe Smith","New York")` is an element of this relation, Ampersand considers the statement `"Joe Smith" livesIn "New York"` to be true. So all pairs in a relation represent ***facts***, i.e. true statements.

## Language that makes sense to the business

Ampersand takes a pragmatic stance on truth: You model only things that make sense to the business. This [video clip](https://player.ou.nl/wowzaportlets/#!production/VDvSFqQ) illustrates the distinction between sensible and senseless statements. A sensible statement (we say: "It makes sense.") is a statement that can be true or false. Sentences that are not sensible (we can say: it is non-sense) are to be avoided. The Ampersand type system helps you to make sensible statements only.

## Truth in context

Truth always has context. If we say "Jack was married to Jackie", this statement is true in a [context](/documentation/the-language-ampersand/context.md) where "Jack" refers to the 35th president of the United States, John F. Kennedy. However, this statement is not true in a context where there is no Jack. And in a context where marriage doesn't exist, this statement makes no sense.