diff --git a/analyzer/argument.go b/analyzer/argument.go
index aa333df..629f7ae 100644
--- a/analyzer/argument.go
+++ b/analyzer/argument.go
@@ -15,6 +15,7 @@ type Argument interface {
 	// FloatLiteral
 	// StringLiteral
 
+	What () (what Type)
 	ToString (indent int) (output string)
 	canBePassedAs (what Type) (allowed bool)
 }
diff --git a/analyzer/common-errors.go b/analyzer/common-errors.go
new file mode 100644
index 0000000..c8c5581
--- /dev/null
+++ b/analyzer/common-errors.go
@@ -0,0 +1,8 @@
+package analyzer
+
+func typeMismatchErrorMessage (source Type, destination Type) (message string) {
+	message += source.Describe()
+	message += " cannot be used as "
+	message += destination.Describe()
+	return
+}
diff --git a/analyzer/literals.go b/analyzer/literals.go
index d4156d7..50a1f15 100644
--- a/analyzer/literals.go
+++ b/analyzer/literals.go
@@ -14,6 +14,13 @@ func (literal IntLiteral) ToString (indent int) (output string) {
 	return
 }
 
+// What returns the type of the argument
+func (literal IntLiteral) What () (what Type) {
+	what.actual = &PrimitiveI64
+	what.length = 1
+	return
+}
+
 // canBePassedAs returns true if this literal can be implicitly cast to the
 // specified type, and false if it can't.
 func (literal IntLiteral) canBePassedAs (what Type) (allowed bool) {
@@ -43,6 +50,13 @@ func (literal UIntLiteral) ToString (indent int) (output string) {
 	return
 }
 
+// What returns the type of the argument
+func (literal UIntLiteral) What () (what Type) {
+	what.actual = &PrimitiveU64
+	what.length = 1
+	return
+}
+
 // canBePassedAs returns true if this literal can be implicitly cast to the
 // specified type, and false if it can't.
 func (literal UIntLiteral) canBePassedAs (what Type) (allowed bool) {
@@ -71,6 +85,13 @@ func (literal UIntLiteral) canBePassedAs (what Type) (allowed bool) {
 	return
 }
 
+// What returns the type of the argument
+func (literal FloatLiteral) What () (what Type) {
+	what.actual = &PrimitiveF64
+	what.length = 1
+	return
+}
+
 // ToString outputs the data in the argument as a string.
 func (literal FloatLiteral) ToString (indent int) (output string) {
 	output += doIndent(indent, fmt.Sprint("arg float ", literal, "\n"))
@@ -95,6 +116,13 @@ func (literal FloatLiteral) canBePassedAs (what Type) (allowed bool) {
 	return
 }
 
+// What returns the type of the argument
+func (literal StringLiteral) What () (what Type) {
+	what.actual = &BuiltInString
+	what.length = 1
+	return
+}
+
 // ToString outputs the data in the argument as a string.
 func (literal StringLiteral) ToString (indent int) (output string) {
 	output += doIndent(indent, fmt.Sprint("arg string \"", literal, "\"\n"))
diff --git a/analyzer/type-section.go b/analyzer/type-section.go
index eaa09b0..2bc7854 100644
--- a/analyzer/type-section.go
+++ b/analyzer/type-section.go
@@ -80,12 +80,16 @@ func (analyzer AnalysisOperation) analyzeTypeSection () (
 		outputSection.argument,
 		err = analyzer.analyzeArgument(inputSection.Argument())
 		if err != nil { return }
+
+		// type check default value
 		if !outputSection.argument.canBePassedAs(outputSection.what) {
-			
+			err = inputSection.Argument().NewError (
+				typeMismatchErrorMessage (
+					outputSection.argument.What(),
+					outputSection.what),
+				infoerr.ErrorKindError)
+			return
 		}
-		// TODO: type check default value. possibly add a method to
-		// Argument that takes in a type and determines whether the
-		// argument can fit to it.
 	}
 
 	// TODO: analyze members
diff --git a/analyzer/type.go b/analyzer/type.go
index 70d1530..ebdf641 100644
--- a/analyzer/type.go
+++ b/analyzer/type.go
@@ -1,6 +1,7 @@
 package analyzer
 
-// import "git.tebibyte.media/arf/arf/types"
+import "fmt"
+import "path/filepath"
 import "git.tebibyte.media/arf/arf/parser"
 import "git.tebibyte.media/arf/arf/infoerr"
 
@@ -204,3 +205,63 @@ func (analyzer AnalysisOperation) analyzeType (
 	
 	return
 }
+
+// Describe provides a human readable description of the type. The value of this
+// should not be computationally analyzed.
+func (what Type) Describe () (description string) {
+	if what.kind == TypeKindBasic {
+		actual := what.actual
+		switch actual {
+		case &PrimitiveF32:
+			description += "F32"
+		case &PrimitiveF64:
+			description += "F64"
+		case &PrimitiveFunc:
+			description += "Func"
+		case &PrimitiveFace:
+			description += "Face"
+		case &PrimitiveObj:
+			description += "Obj"
+		case &PrimitiveU64:
+			description += "U64"
+		case &PrimitiveU32:
+			description += "U32"
+		case &PrimitiveU16:
+			description += "U16"
+		case &PrimitiveU8:
+			description += "U8"
+		case &PrimitiveI64:
+			description += "I64"
+		case &PrimitiveI32:
+			description += "I32"
+		case &PrimitiveI16:
+			description += "I16"
+		case &PrimitiveI8:
+			description += "I8"
+		case &PrimitiveUInt:
+			description += "UInt"
+		case &PrimitiveInt:
+			description += "Int"
+		
+		case nil:
+			panic("invalid state: Type.actual is nil")
+
+		default:
+			locator := actual.locator()
+			description +=
+				filepath.Base(locator.modulePath) +
+				"." + locator.name
+			return
+		}
+	} else {
+		description += "{"
+		description += what.points.Describe()
+		description += "}"
+	}
+
+	if what.length > 0 {
+		description += fmt.Sprint(":", what.length)
+	}
+
+	return
+}