diff --git a/gtsam/symbolic/SymbolicConditional.cpp b/gtsam/symbolic/SymbolicConditional.cpp
index f0d9944b2..eb8a95cff 100644
--- a/gtsam/symbolic/SymbolicConditional.cpp
+++ b/gtsam/symbolic/SymbolicConditional.cpp
@@ -33,4 +33,10 @@ bool SymbolicConditional::equals(const This& c, double tol) const {
   return BaseFactor::equals(c) && BaseConditional::equals(c);
 }
 
+/* ************************************************************************* */
+double SymbolicConditional::logProbability(const HybridValues& c) const {
+  throw std::runtime_error("SymbolicConditional::logProbability is not implemented");
+}
+
+
 }  // namespace gtsam
diff --git a/gtsam/symbolic/SymbolicConditional.h b/gtsam/symbolic/SymbolicConditional.h
index 4f4917950..8970902d7 100644
--- a/gtsam/symbolic/SymbolicConditional.h
+++ b/gtsam/symbolic/SymbolicConditional.h
@@ -95,13 +95,10 @@ namespace gtsam {
       return FromIteratorsShared(keys.begin(), keys.end(), nrFrontals);
     }
 
-    ~SymbolicConditional() override {}
-
     /// Copy this object as its actual derived type.
     SymbolicFactor::shared_ptr clone() const { return boost::make_shared<This>(*this); }
 
     /// @}
-
     /// @name Testable
     /// @{
 
@@ -114,6 +111,19 @@ namespace gtsam {
     bool equals(const This& c, double tol = 1e-9) const;
 
     /// @}
+    /// @name HybridValues methods.
+    /// @{
+
+    /**
+     * logProbability throws exception, symbolic.
+     */
+    double logProbability(const HybridValues& x) const override;
+
+    using Conditional::evaluate; // Expose evaluate(const HybridValues&) method..
+    using Conditional::operator(); // Expose evaluate(const HybridValues&) method..
+    using SymbolicFactor::error; // Expose error(const HybridValues&) method..
+
+    /// @}
 
   private:
     /** Serialization function */
diff --git a/gtsam/symbolic/SymbolicFactor.cpp b/gtsam/symbolic/SymbolicFactor.cpp
index 327de0c10..671b71f93 100644
--- a/gtsam/symbolic/SymbolicFactor.cpp
+++ b/gtsam/symbolic/SymbolicFactor.cpp
@@ -26,6 +26,11 @@ using namespace std;
 
 namespace gtsam {
 
+  /* ************************************************************************* */
+  double SymbolicFactor::error(const HybridValues& c) const {
+    throw std::runtime_error("SymbolicFactor::error is not implemented");
+  }
+
   /* ************************************************************************* */
   std::pair<boost::shared_ptr<SymbolicConditional>, boost::shared_ptr<SymbolicFactor> >
     EliminateSymbolic(const SymbolicFactorGraph& factors, const Ordering& keys)
diff --git a/gtsam/symbolic/SymbolicFactor.h b/gtsam/symbolic/SymbolicFactor.h
index 208efafb8..12b3374c8 100644
--- a/gtsam/symbolic/SymbolicFactor.h
+++ b/gtsam/symbolic/SymbolicFactor.h
@@ -30,6 +30,7 @@ namespace gtsam {
 
   // Forward declarations
   class SymbolicConditional;
+  class HybridValues;
   class Ordering;
 
   /** SymbolicFactor represents a symbolic factor that specifies graph topology but is not
@@ -46,7 +47,7 @@ namespace gtsam {
     /** Overriding the shared_ptr typedef */
     typedef boost::shared_ptr<This> shared_ptr;
 
-    /// @name Standard Interface
+    /// @name Standard Constructors
     /// @{
 
     /** Default constructor for I/O */
@@ -106,10 +107,9 @@ namespace gtsam {
     }
 
     /// @}
-
     /// @name Advanced Constructors
     /// @{
-  public:
+  
     /** Constructor from a collection of keys */
     template<typename KEYITERATOR>
     static SymbolicFactor FromIterators(KEYITERATOR beginKey, KEYITERATOR endKey) {
@@ -143,6 +143,9 @@ namespace gtsam {
     /// @name Standard Interface
     /// @{
 
+    /// The `error` method throws an exception.
+    double error(const HybridValues& c) const override;
+
     /** Eliminate the variables in \c keys, in the order specified in \c keys, returning a
      *  conditional and marginal. */
     std::pair<boost::shared_ptr<SymbolicConditional>, boost::shared_ptr<SymbolicFactor> >