  In-Context Learning (ICL) and Instruction Tuning (IT) are two primary
paradigms of adopting Large Language Models (LLMs) to downstream applications.
However, they are significantly different. In ICL, a set of demonstrations are
provided at inference time but the LLM's parameters are not updated. In IT, a
set of demonstrations are used to tune LLM's parameters in training time but no
demonstrations are used at inference time. Although a growing body of
literature has explored ICL and IT, studies on these topics have largely been
conducted in isolation, leading to a disconnect between these two paradigms. In
this work, we explore the relationship between ICL and IT by examining how the
hidden states of LLMs change in these two paradigms. Through carefully designed
experiments conducted with LLaMA-2 (7B and 13B), we find that ICL is implicit
IT. In other words, ICL changes an LLM's hidden states as if the demonstrations
were used to instructionally tune the model. Furthermore, the convergence
between ICL and IT is largely contingent upon several factors related to the
provided demonstrations. Overall, this work offers a unique perspective to
explore the connection between ICL and IT and sheds light on understanding the
behaviors of LLM.
