1 Introduction

2 Settings and Learning Modes of CL  
2.1 CL Settings  
2.2 Learning Modes  

3 NLP Tasks in CL  
3.1 Types of Tasks  
3.2 CL Formulation of NLP Problems  

4 Approaches for Continual Learning  
4.1 Approaches for CF Prevention  
4.2 Approaches for Knowledge Transfer  
4.3 Dealing with Inter-task Class Separation  

5 Observations and Future Directions  

6 Conclusion