  The field of vision-and-language (VL) understanding has made unprecedented
progress with end-to-end large pre-trained VL models (VLMs). However, they
still fall short in zero-shot reasoning tasks that require multi-step
inferencing. To achieve this goal, previous works resort to a
divide-and-conquer pipeline. In this paper, we argue that previous efforts have
several inherent shortcomings: 1) They rely on domain-specific sub-question
decomposing models. 2) They force models to predict the final answer even if
the sub-questions or sub-answers provide insufficient information. We address
these limitations via IdealGPT, a framework that iteratively decomposes VL
reasoning using large language models (LLMs). Specifically, IdealGPT utilizes
an LLM to generate sub-questions, a VLM to provide corresponding sub-answers,
and another LLM to reason to achieve the final answer. These three modules
perform the divide-and-conquer procedure iteratively until the model is
confident about the final answer to the main question. We evaluate IdealGPT on
multiple challenging VL reasoning tasks under a zero-shot setting. In
particular, our IdealGPT outperforms the best existing GPT-4-like models by an
absolute 10% on VCR and 15% on SNLI-VE. Code is available at
https://github.com/Hxyou/IdealGPT
