Abusive language detection relies on understanding different levels of intensity, expressiveness and targeted groups, which requires commonsense reasoning, world knowledge and linguistic nuances that evolve over time. Here, we frame the problem as a knowledge-guided learning task, and demonstrate that LLMs’ implicit knowledge without an accurate strategy is not suitable for multi-class detection nor explanation generation. We publicly release GLlama Alarm, the knowledge-Guided version of Llama-2 instruction fine-tuned for multi-class abusive language detection and explanation generation. By being fine-tuned on structured explanations and external reliable knowledge sources, our model mitigates bias and generates explanations that are relevant to the text and coherent with human reasoning, with an average 48.76% better alignment with human judgment according to our expert survey.

Explainable abusive language detection has proven to help both users and content moderators, and recent research has focused on prompting LLMs to generate explanations for why a specific text is hateful. Yet, understanding the alignment of these generated explanations with human expectations and judgements is far from being solved. In this paper, we design a before-and-after study recruiting AI experts to evaluate the usefulness and trustworthiness of LLM-generated explanations for abusive language detection tasks, investigating multiple LLMs and learning strategies. Our experiments show that expectations in terms of usefulness and trustworthiness of LLM-generated explanations are not met, as their ratings decrease by 47.78% and 64.32%, respectively, after treatment. Further, our results suggest caution in using LLMs for explanation generation of abusive language detection due to (i) their cultural bias, and (ii) difficulty in reliably evaluating them with empirical metrics. In light of our results, we provide three recommendations to use LLMs responsibly for explainable abusive language detection.

We present a study on the integration of time-sensitive information in lexicon-based offensive language detection systems. Our focus is on Offenseval sub-task A, aimed at detecting offensive tweets. We apply a semantic change detection algorithm over a short time span of two years to detect words whose semantics has changed and we focus particularly on those words that acquired or lost an offensive meaning between 2019 and 2020. Using the output of this semantic change detection approach, we train an SVM classifier on the Offenseval 2019 training set. We build on the already competitive SINAI system submitted to Offenseval 2019 by adding new lexical features, including those that capture the change in usage of words and their association with emerging offensive usages. We discuss the challenges, opportunities and limitations of integrating semantic change detection in offensive language detection models. Our work draws attention to an often neglected aspect of offensive language, namely that the meanings of words are constantly evolving and that NLP systems that account for this change can achieve good performance even when not trained on the most recent training data.