This week, I am going to share my amazement and doubts about what could be called the surprising multilinguality of large language models. By large language models, I mean the really large ones that I can hardly run myself, trained on huge, hardly curated data and thus harbouring the worst societal demons, but also having many fascinating properties. Here, I would like to feature three papers that make me think about the properties of the models.
1. Finetuning to other languages. This paper from the University of Groningen published in the Findings of ACL 2021 shows a simple way how the English GPT-2 model can be finetuned to other languages. They do it in two steps: first, they create a vocabulary for the new language and only learn the embeddings (as if they just replaced the lexicon of otherwise universal grammar), second, they finetune the rest of the model. The results are much better than training a model from scratch.
2. Unsupervised translation. The GPT-3 model showed some ability to do zero-shot or few-shot machine translation, but translation performance was not that great (although it is still fascinating that it works). In this recent pre-print by OpenAI, they did the quite obvious thing: They start with GPT-3 zero-shot capabilities and do iterative back-translation that is commonly done in unsupervised MT. In this way, there were able to beat state-of-the-art approaches that rely on multilingual pre-training. On the other hand, they start with a much larger model and use French as the target language. I am sure the results would be much worse if they decided to translate a truly low-resource language, where unsupervised MT is of much higher value.
3. Few-shot crosslingual learning. In this recent pre-print by Google Brain, they took the T5 model and GPTNeo (which should be similar or even better than GPT-3) and tried the few-shot learning setup known from the GPT-3 paper. The model is given a few examples, how it is supposed to perform a task (e.g., assigning labels to sentences), then it is given an unlabeled sentence, and the model is supposed to continue by generating the proper label. The surprise of this paper is that it works even if the examples are in a different language than English.
All these results make me wonder if it is possible that with this amount of parameters and training data, the model learns something fundamental about the language, something all languages have in common. The first thing that would come to my mind is of course Chomsky’s dreamed-of language device capable of learning any language, but it would mean admitting that syntactic structures are more real than the real sentences and that compositionality rules the world, which is very hard to agree with. But still, can the models learn something fundamental about the human language? The answer is probably not, there is probably some simple explanation we are just not aware of, but the question is still very tempting. Rigorous answering this question is very difficult. There are at least two hypotheses that need to be disproved:
Data contamination hypothesis. There are other languages in the training data. Perhaps, it learns the other languages from the training data. The GPT-3 paper explicitly admits, there are sentences in other languages, so they can try zero-shot MT.
Rejoinder: Still, the large majority of the data is in English. If only a handful of examples can make the models work cross-lingually does it merely confirm that the models learn something very general if only a weak training signal can help?
Meta-language hypothesis. This is probably a crazy one. But still, LMs can work partially as knowledge bases. Perhaps just talking about languages (the entire Wikipedia is in the training data) makes the model know plenty of stuff about the languages. Sort of like if a brilliant person would read the entire Wikipedia and remember everything. However, remembering the knowledge about language and using the knowledge are two totally different things, which makes this hypothesis very implausible.
Rejoinder: If this hypothesis were true, it would mean we basically have AGI (which is very unlikely, though). Who cares about universal language structure, if we have AGI!
Finding an answer would require careful curation of the training data, which is hardly feasible in the required amounts. (And those who are interested in large LMs have the money for that have other priorities.) Also, running the contrastive experiments would probably require its own power plant, and such experiments might not be the best use of electrical energy most people can imagine.
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author = "Jindřich Libovický",
title = "Jindřich's Blog -- Machine Translation Weekly 90: The Surprising Multinguality of Large Language Models",
year = "2021",
month = oct,
url = "https://jlibovicky.github.io/2021/10/18/MT-Weekly-Mutilinguality-of-large-LMs",
note = "Online, Accessed: 06.02. 2024"