Why can't I use an abstract class like an interface at runtime.

I get the output:

```
1>c:\program files (x86)\microsoft visual studio 12.0\vc\include\xmemory0(615): error C2259: 'Creature' : cannot instantiate abstract class
1>          due to following members:
1>          'std::string Creature::Move(std::vector<std::string,std::allocator<_Ty>> &)' : is abstract
1>          with
1>          [
1>              _Ty=std::string
1>          ]

1>          visual studio 2013\projects\cpp_demo\cpp_demo\creature.h(9) : see declaration of 'Creature::Move'
1>          c:\program files (x86)\microsoft visual studio 12.0\vc\include\xmemory0(614) : while compiling class template member function 'void std::allocator<_Ty>::construct(_Ty *,const _Ty &)'
1>          with
1>          [
1>              _Ty=Creature
1>          ]

1>          c:\program files (x86)\microsoft visual studio 12.0\vc\include\xmemory0(752) : see reference to function template instantiation 'void std::allocator<_Ty>::construct(_Ty *,const _Ty &)' being compiled
1>          with
1>          [
1>              _Ty=Creature
1>          ]

1>          c:\program files (x86)\microsoft visual studio 12.0\vc\include\type_traits(580) : see reference to class template instantiation 'std::allocator<_Ty>' being compiled
1>          with
1>          [
1>              _Ty=Creature
1>          ]

1>          c:\program files (x86)\microsoft visual studio 12.0\vc\include\vector(650) : see reference to class template instantiation 'std::is_empty<_Alloc>' being compiled
1>          with
1>          [
1>              _Alloc=std::allocator<Creature>
1>          ]

1>          visual studio 2013\projects\cpp_demo\cpp_demo\main.cpp(7) : see reference to class template instantiation 'std::vector<Creature,std::allocator<_Ty>>' being compiled
1>          with
1>          [
1>              _Ty=Creature
1>          ]

```

My code: 

```
int main()
{
    unique_ptr<vector<Creature>> pCreatures(new vector<Creature>);

    unique_ptr<Creature> pHuman(new Human());
    pCreatures->push_back(*pHuman);
}

#include "stdafx.h"
#include "Creature.h"

class Human : public Creature
{
public:
    virtual string Move(vector<string> &log);
};

#include "stdafx.h"
#include "IMove.h"

class Creature : public IMove
{
public:
    virtual string Move(vector<string> &log) = 0;
    virtual string GetState(vector<string> &log);
};

```

Please help.