# Declarations

RuLa has two kinds of variables: **instance variables**, introduced through declarations, and **value variables**, introduced with `:=` inside the assignment part of a rule. This page covers instance variables. For value variables, see [Variables](/rule-language/variables.md).

A declaration does two things at once: it matches one or more instances from the case (a Person, Entity, Contract, etc.) and it defines an instance variable — a short name you can use throughout the rest of the rule to refer to that instance and access its information fields. Each additional declaration matches one more instance, so `p is Person` and `c is Contract` together match one person and one contract.

You need to declare an instance variable before you can use it — an undeclared variable is unknown in RuLa.

```
c is Contract
e is Entity
p is Person, AccountHolder
```

### The Impact of a Declaration

How you formulate a declaration has an impact on what a rule will be about. If, on a [document](/guides/glossary/document.md), you declare these instance variables

```
c is Contract
p is Person
```

that document will need to contain one contract and one person.

Alternatively, if you declare

```
p is Person
```

that document will be about exactly one person. In a [case](/guides/glossary/case.md) that involves not one but three people, the system will require this document three times: once for each person in the case.

However, if you declare

```
p1 is Person
p2 is Person
p3 is Person
```

on a document, that document can contain all three people in the case. It will only be required once.


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