Contrastive Self-Explanation Method (CoSEM): Generating Large Language Model Contrastive Self-Explanations

Abstract

Large language models (LLMs) are widely used tools that assist us by answering various questions. Humans implicitly use contrast as a natural way to think about and seek explanations (i.e., "Why A and not B?"). Explainability is a challenging aspect of LLMs, as we do not truly understand how good the LLM answers are. The challenge is understanding to what extent LLMs can generate effective contrastive self-explanations for users. We introduce the Contrastive Self-Explanation Method (CoSEM) to narrow the gap between LLMs and explainability. It generates contrastive self- explanations and evaluates them through automation and a user study on generality, usefulness, readability, and relevance. Our results indicate that LLMs are capable of generating effective contrastive self-explanations. Lexical analysis of contrastive explanation indicates that explanations are not less general than the text those explain, and semantic analysis shows that more complex models generalize self-explanations more consistently. Although it is challenging to evaluate contrast in self-explanations semantically, user study shows that some models (Llama3-8B) help understand the contrast. Moreover, task selection affects how readable users find the explanations, where more self-explanations on general topics (movie reviews) are more readable than more specific topics (medical diagnoses). Lastly, some models, such as Llama3-8B, excel at generating contrastive self-explanations that contain relevant information regarding input text.