Inference to the Best Explanation in Large Language Models

While Large Language Models (LLMs) have found success in real-world applications, their underlying explanatory process is still poorly understood.This paper proposes IBE-Eval, a framework inspired by philosophical accounts on Inference to the Best Explanation (IBE) to advance the interpretation and evaluation of LLM explanations.IBE-Eval estimates the plausibility of natural language explanations through a combination of explicit logical and linguistic features including: consistency, parsimony, coherence, and uncertainty.Extensive experiments are conducted on Causal Question Answering (CQA), where IBE-Eval is tasked to select the most plausible causal explanation amongst competing ones generated by the LLM (e.g.GPT 3.5 or LLaMA 2).The experiments reveal that IBE-Eval can successfully identify the best explanation with up to 77% accuracy ( 27% above random), improving upon a GPT 3.5-as-a-judge baseline ( +17%) while being intrinsically more efficient and interpretable.Additional analysis suggests that, despite LLM-specific variances, generated explanations tend to conform to IBE criteria and that IBE-Eval is significantly correlated with human judgment, opening up opportunities for future development of automated explanation verification tools. Inference to the Best Explanation (IBE)Selection Criteria Competing Explanations Competing HypothesesPremise 1: I blew into the baloon. Conclusion:The balloon expanded.Premise 2: I pricked the baloon.Conclusion: The balloon expanded. LLM Explanation 1 (E1)Step 1: IF someone blows into a balloon, THEN it can cause the balloon to inflate.Assumption: Blowing air into a balloon increases the amount of air inside it, leading to inflation.Step 2: IF the balloon inflates, THEN it can cause the balloon to expand.Assumption: When a balloon inflates, it stretches and expands in size.Therefore, since I blew into the balloon, it caused the balloon to inflate, which resulted in its expansion. Explanation 2 (E2)Step 1: IF a balloon is pricked, THEN the balloon may deflate.Assumption: Pricking a balloon can cause it to lose air and deflate.Step 2: IF a balloon deflates, THEN there is a decrease in air pressure inside the balloon.Assumption: When a balloon deflates, the air pressure inside the balloon decreases.Step 3: IF there is a decrease in air pressure inside the balloon, THEN the external air pressure will cause the balloon to expand.Assumption: When the air pressure inside a balloon is lower than the external air pressure, the balloon will expand.Therefore, since the balloon was pricked, it may have deflated, resulting in a decrease in air pressure inside the balloon, causing the external air pressure to make the balloon expand Causal Question The balloon expanded.What was the cause?A) I blew into it.B) I pricked it.