The Unlocking Spell on Base LLMs: Rethinking Alignment via In-Context
  Learning
Authors: name: Bill Yuchen Lin; name: Abhilasha Ravichander; name: Ximing Lu; name: Nouha Dziri; name: Melanie Sclar; name: Khyathi Chandu; name: Chandra Bhagavatula; name: Yejin Choi
Published: 2023-12-04 00:46:11

Abstract: The alignment tuning process of large language models (LLMs) typically
involves instruction learning through supervised fine-tuning (SFT) and
preference tuning via reinforcement learning from human feedback (RLHF). A
recent study, LIMA (Zhou et al. 2023), shows that using merely 1K examples for
SFT can achieve significant alignment performance as well, suggesting that the
effect of alignment tuning might be "superficial." This raises questions about
how exactly the alignment tuning transforms a base LLM.
  We analyze the effect of alignment tuning by examining the token distribution
shift between base LLMs and their aligned counterpart. Our findings reveal that
base LLMs and their alignment-tuned versions perform nearly identically in
decoding on the majority of token positions. Most distribution shifts occur
with stylistic tokens. These direct evidence strongly supports the Superficial
Alignment Hypothesis suggested by LIMA.
  Based on these findings, we rethink the alignment of LLMs by posing the
research question: how effectively can we align base LLMs without SFT or RLHF?
To address this, we introduce a simple, tuning-free alignment method, URIAL.
URIAL achieves effective alignment purely through in-context learning (ICL)
with base LLMs, requiring as few as three constant stylistic examples and a
system prompt. We conduct a fine-grained and interpretable evaluation on a
diverse set of examples, named JUST-EVAL-INSTRUCT. Results demonstrate that
base LLMs with URIAL can match or even surpass the performance of LLMs aligned
with SFT or SFT+RLHF. We show that the gap between tuning-free and tuning-based
alignment methods can be significantly reduced through strategic prompting and
ICL. Our findings on the superficial nature of alignment tuning and results
with URIAL suggest that deeper analysis and theoretical understanding of
alignment is crucial to future LLM research.