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Transformers as Soft Reasoners over Language (2002.05867v2)

Published 14 Feb 2020 in cs.CL and cs.AI

Abstract: Beginning with McCarthy's Advice Taker (1959), AI has pursued the goal of providing a system with explicit, general knowledge and having the system reason over that knowledge. However, expressing the knowledge in a formal (logical or probabilistic) representation has been a major obstacle to this research. This paper investigates a modern approach to this problem where the facts and rules are provided as natural language sentences, thus bypassing a formal representation. We train transformers to reason (or emulate reasoning) over these sentences using synthetically generated data. Our models, that we call RuleTakers, provide the first empirical demonstration that this kind of soft reasoning over language is learnable, can achieve high (99%) accuracy, and generalizes to test data requiring substantially deeper chaining than seen during training (95%+ scores). We also demonstrate that the models transfer well to two hand-authored rulebases, and to rulebases paraphrased into more natural language. These findings are significant as it suggests a new role for transformers, namely as limited "soft theorem provers" operating over explicit theories in language. This in turn suggests new possibilities for explainability, correctability, and counterfactual reasoning in question-answering.

Citations (322)

Summary

  • The paper demonstrates that transformer models can emulate logical reasoning over natural language rules without relying on formal logic representations.
  • The authors develop RuleTakers by training transformers on synthetic datasets with varying inference depths to assess reasoning proficiency.
  • Empirical results show near-perfect in-domain performance and strong zero-shot transfer, highlighting scalable and adaptable language-based reasoning.

Overview of "Transformers as Soft Reasoners over Language"

The paper by Peter Clark, Oyvind Tafjord, and Kyle Richardson examines the capability of transformer models to perform reasoning tasks over rules expressed in natural language. The authors introduce the concept of "soft reasoning," positioning transformers as "soft theorem provers" that operate without an explicit formal logical representation. They focus on the RuleTakers models, a novel approach using transformers trained with synthetically generated data to emulate reasoning processes over linguistic expressions.

Motivation and Background

Since the inception of AI, there has been a desire to create systems that can use explicit knowledge to reason. Classical AI confronted the challenge of converting knowledge into formal logical representations, which proved difficult and limited the applicability of such systems. The paper revisits McCarthy's 1959 concept of the "Advice Taker" with a contemporary twist: bypassing formal logic representations altogether and employing language-based reasoning.

Methodology

The authors generate datasets containing English-language representations of logical theories involving facts and rules. These datasets vary according to the depth of reasoning required to derive answers. The models, coined "RuleTakers," are evaluated on their ability to learn from these datasets and efficiently reason to reach conclusions regarding the questions posed.

Key Aspects of the Method:

  • Dataset Construction: The data used to train RuleTakers is created by generating theories in logical form, forward-chaining inferences, and converting these logical statements into simple English sentences. This ensures both rigour in logical grounding and accessibility in linguistic form.
  • Depth of Inference: Datasets are partitioned by the maximum depth of reasoning required (D=0, D≤1, D≤2, D≤3, DMax), enabling the evaluation of models at increasing complexity levels.
  • Model Training and Testing: RuleTakers, based on the RoBERTa transformer, are trained and tested on these datasets for their proficiency in both in-domain and out-of-domain reasoning tasks.

Results

The empirical results reveal several noteworthy patterns:

  • Accuracy in Depth-Specific Tasks: RuleTakers achieve near-perfect accuracy within their training distributions, demonstrating that the approach scales well with increasing levels of inference depth.
  • Zero-shot Transfer Performance: Testing on hand-crafted rulebases underscores the model's robustness, achieving high accuracy even when the scenarios and vocabulary differ from the training data. This indicates a degree of generalization and adaptability.
  • Paraphrased Language Reasoning: When applied to paraphrased rule sets, the RuleTaker models exhibit significant resilience, pointing towards potential applicability in more natural, less structured language contexts.

Implications and Future Work

The practical implications of these findings are profound. The ability to train models for language-based reasoning opens avenues for:

  • Explainability and Correctability: By structuring knowledge explicitly, models can offer explanations for their conclusions and corrections post-error detection, potentially enabling more controllable machine learning systems.
  • Enhanced Question-Answering Capabilities: Operating without the need for a rigid formalism, these models can integrate with existing question-answering frameworks, providing sophisticated reasoning capabilities that leverage explicit knowledge.
  • Broader AI Applications: This research suggests a tangible pathway to integrating reasoning abilities across numerous AI applications, particularly in domains requiring fact inference and rule-based reasoning.

Future Research Directions:

  • Extending robustness to more diverse and complex rule expressions,
  • Exploring the integration of more nuanced natural language processing tasks,
  • Bridging the gap between synthetic reasoning datasets and real-world complexities,
  • Evaluating the impact of pre-training on model performance across varied linguistic scenarios.

Overall, while the work showcases promising developments in AI reasoning, it also sets a foundation for continued exploration into more adaptable, reliable language-based reasoning systems. The paper's conclusions suggest a transformed perspective on how AI might emulate deductive processes without rigid formalisms, unlocking more flexible interactions with human language.

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