How does "chain-of-thought" prompting work?

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Chain-of-thought prompting refers to techniques which make a language model generate intermediate reasoning steps in its output. These prompting methods can help a model give accurate answers to questions that require multiple reasoning steps. For example:

Input:

Take the last letters of the name “Lady Gaga” and concatenate them.

Model Output (without intermediate reasoning steps):

The answer is “ya”.

Model Output (with intermediate reasoning steps):

The last letter of “Lady” is “y”. The last letter of “Gaga” is “a”. Concatenating them gives “ya”. So the answer is “ya”.

Chain-of-thought prompting can be done via few-shot prompting (i.e., giving the model examples of chain-of-thought reasoning for it to emulate) or zero-shot prompting (i.e., asking the model in the input prompt to "think step-by-step" in the input prompt).

The difference between standard prompting and chain-of-thought prompting for an arithmetic reasoning problem is illustrated in the figure below.

Source - Wei et al., Chain-of-Thought Prompting Elicits Reasoning in Large Language Models (2023)

Chain-of-thought prompting works especially well on difficult natural language processing tasks like multi-step arithmetic, symbolic reasoning, and common-sense reasoning. This prompting method can also be automated using LLMs to generate prompts and evaluate responses.

A model’s ability to break down complex problems into intermediate steps is referred to as “chain-of-thought reasoning”, which emerges from increasing model scale. However, the explanations a model generates in chain-of-thought reasoning might not represent its actual reasoning. This implies that chain-of-thought prompting cannot be relied upon to provide a faithfully interpretable window into the model’s actual reasoning.

The main limitation of chain-of-thought prompting is that it generalizes poorly from the examples in the input prompt to harder problems. Further work on techniques like “least-to-most prompting” has tried to address this limitation.