diff --git a/src/Illuminate/Support/Traits/Conditional.php b/src/Illuminate/Support/Traits/Conditional.php
new file mode 100644
index 000000000000..0b76e65e48c1
--- /dev/null
+++ b/src/Illuminate/Support/Traits/Conditional.php
@@ -0,0 +1,40 @@
+<?php
+
+namespace Illuminate\Support\Traits;
+
+trait Conditional
+{
+    /**
+     * Apply the callback if the given "value" is true.
+     *
+     * @param  mixed  $value
+     * @param  callable  $callback
+     * @param  callable|null  $default
+     *
+     * @return mixed
+     */
+    public function when($value, $callback, $default = null)
+    {
+        if ($value) {
+            return $callback($this, $value) ?: $this;
+        } elseif ($default) {
+            return $default($this, $value) ?: $this;
+        }
+
+        return $this;
+    }
+
+    /**
+     * Apply the callback if the given "value" is false.
+     *
+     * @param  mixed  $value
+     * @param  callable  $callback
+     * @param  callable|null  $default
+     *
+     * @return mixed
+     */
+    public function unless($value, $callback, $default = null)
+    {
+        return $this->when(! $value, $callback, $default);
+    }
+}
diff --git a/src/Illuminate/Validation/Rules/Dimensions.php b/src/Illuminate/Validation/Rules/Dimensions.php
index e2326c7732b1..d390b8c8823b 100644
--- a/src/Illuminate/Validation/Rules/Dimensions.php
+++ b/src/Illuminate/Validation/Rules/Dimensions.php
@@ -2,8 +2,12 @@
 
 namespace Illuminate\Validation\Rules;
 
+use Illuminate\Support\Traits\Conditional;
+
 class Dimensions
 {
+    use Conditional;
+
     /**
      * The constraints for the dimensions rule.
      *
diff --git a/src/Illuminate/Validation/Rules/Exists.php b/src/Illuminate/Validation/Rules/Exists.php
index 72c378600964..59df5f3da0ee 100644
--- a/src/Illuminate/Validation/Rules/Exists.php
+++ b/src/Illuminate/Validation/Rules/Exists.php
@@ -2,9 +2,12 @@
 
 namespace Illuminate\Validation\Rules;
 
+use Illuminate\Support\Traits\Conditional;
+
 class Exists
 {
     use DatabaseRule;
+    use Conditional;
 
     /**
      * Convert the rule to a validation string.
diff --git a/src/Illuminate/Validation/Rules/Password.php b/src/Illuminate/Validation/Rules/Password.php
index eddb897f43c4..a6d4e6b8c18e 100644
--- a/src/Illuminate/Validation/Rules/Password.php
+++ b/src/Illuminate/Validation/Rules/Password.php
@@ -8,10 +8,13 @@
 use Illuminate\Contracts\Validation\UncompromisedVerifier;
 use Illuminate\Support\Arr;
 use Illuminate\Support\Facades\Validator;
+use Illuminate\Support\Traits\Conditional;
 use InvalidArgumentException;
 
 class Password implements Rule, DataAwareRule
 {
+    use Conditional;
+
     /**
      * The data under validation.
      *
diff --git a/src/Illuminate/Validation/Rules/Unique.php b/src/Illuminate/Validation/Rules/Unique.php
index 64e910240382..426c313142f6 100644
--- a/src/Illuminate/Validation/Rules/Unique.php
+++ b/src/Illuminate/Validation/Rules/Unique.php
@@ -3,10 +3,12 @@
 namespace Illuminate\Validation\Rules;
 
 use Illuminate\Database\Eloquent\Model;
+use Illuminate\Support\Traits\Conditional;
 
 class Unique
 {
     use DatabaseRule;
+    use Conditional;
 
     /**
      * The ID that should be ignored.
diff --git a/tests/Validation/ValidationDimensionsRuleTest.php b/tests/Validation/ValidationDimensionsRuleTest.php
index 469d060e9bd8..29d518a16081 100644
--- a/tests/Validation/ValidationDimensionsRuleTest.php
+++ b/tests/Validation/ValidationDimensionsRuleTest.php
@@ -29,5 +29,14 @@ public function testItCorrectlyFormatsAStringVersionOfTheRule()
         $rule = Rule::dimensions()->minWidth(300)->minHeight(400);
 
         $this->assertSame('dimensions:min_width=300,min_height=400', (string) $rule);
+
+        $rule = Rule::dimensions()
+            ->when(true, function ($rule) {
+                $rule->height('100');
+            })
+            ->unless(true, function ($rule) {
+                $rule->width('200');
+            });
+        $this->assertSame('dimensions:height=100', (string) $rule);
     }
 }
diff --git a/tests/Validation/ValidationExistsRuleTest.php b/tests/Validation/ValidationExistsRuleTest.php
index e0039d6c6cfd..77918ce3992a 100644
--- a/tests/Validation/ValidationExistsRuleTest.php
+++ b/tests/Validation/ValidationExistsRuleTest.php
@@ -116,6 +116,35 @@ public function testItChoosesValidRecordsUsingWhereNotInRule()
         $this->assertTrue($v->passes());
     }
 
+    public function testItChoosesValidRecordsUsingConditionalModifiers()
+    {
+        $rule = new Exists('users', 'id');
+        $rule->when(true, function ($rule) {
+            $rule->whereNotIn('type', ['foo', 'bar']);
+        });
+        $rule->unless(true, function ($rule) {
+            $rule->whereNotIn('type', ['baz', 'other']);
+        });
+
+        User::create(['id' => '1', 'type' => 'foo']);
+        User::create(['id' => '2', 'type' => 'bar']);
+        User::create(['id' => '3', 'type' => 'baz']);
+        User::create(['id' => '4', 'type' => 'other']);
+
+        $trans = $this->getIlluminateArrayTranslator();
+        $v = new Validator($trans, [], ['id' => $rule]);
+        $v->setPresenceVerifier(new DatabasePresenceVerifier(Eloquent::getConnectionResolver()));
+
+        $v->setData(['id' => 1]);
+        $this->assertFalse($v->passes());
+        $v->setData(['id' => 2]);
+        $this->assertFalse($v->passes());
+        $v->setData(['id' => 3]);
+        $this->assertTrue($v->passes());
+        $v->setData(['id' => 4]);
+        $this->assertTrue($v->passes());
+    }
+
     public function testItChoosesValidRecordsUsingWhereNotInAndWhereNotInRulesTogether()
     {
         $rule = new Exists('users', 'id');
diff --git a/tests/Validation/ValidationPasswordRuleTest.php b/tests/Validation/ValidationPasswordRuleTest.php
index 5d16de98f224..d484226e2d57 100644
--- a/tests/Validation/ValidationPasswordRuleTest.php
+++ b/tests/Validation/ValidationPasswordRuleTest.php
@@ -41,6 +41,25 @@ public function testMin()
         $this->passes(new Password(8), ['88888888']);
     }
 
+    public function testConditional()
+    {
+        $is_privileged_user = true;
+        $rule = (new Password(8))->when($is_privileged_user, function ($rule) {
+            $rule->symbols();
+        });
+
+        $this->fails($rule, ['aaaaaaaa', '11111111'], [
+            'The my password must contain at least one symbol.',
+        ]);
+
+        $is_privileged_user = false;
+        $rule = (new Password(8))->when($is_privileged_user, function ($rule) {
+            $rule->symbols();
+        });
+
+        $this->passes($rule, ['aaaaaaaa', '11111111']);
+    }
+
     public function testMixedCase()
     {
         $this->fails(Password::min(2)->mixedCase(), ['nn', 'MM'], [
diff --git a/tests/Validation/ValidationUniqueRuleTest.php b/tests/Validation/ValidationUniqueRuleTest.php
index c967ab7c077c..c1545887db02 100644
--- a/tests/Validation/ValidationUniqueRuleTest.php
+++ b/tests/Validation/ValidationUniqueRuleTest.php
@@ -40,6 +40,16 @@ public function testItCorrectlyFormatsAStringVersionOfTheRule()
         $rule->where('foo', 'bar');
         $this->assertSame('unique:table,column,"Taylor, Otwell",id_column,foo,"bar"', (string) $rule);
 
+        $rule = new Unique(EloquentModelStub::class, 'column');
+        $rule->where('foo', 'bar');
+        $rule->when(true, function ($rule) {
+            $rule->ignore('Taylor, Otwell', 'id_column');
+        });
+        $rule->unless(true, function ($rule) {
+            $rule->ignore('Chris', 'id_column');
+        });
+        $this->assertSame('unique:table,column,"Taylor, Otwell",id_column,foo,"bar"', (string) $rule);
+
         $rule = new Unique('table', 'column');
         $rule->ignore('Taylor, Otwell"\'..-"', 'id_column');
         $rule->where('foo', 'bar');