Acknowledgements
This work, which began in the summer of 2016, owes a lot to several people, whom I want to thank here: Ch. de Lamberterie, R. Meyer, D. Petit, G.-J. Pinault and F. Pontani for their remarks and suggestions on the manuscript, from which the text greatly benefited. O. Hackstein, S. Neri and the participants of the Indogermanisches Seminar in Munich, LMU, before whom I presented parts of this work in a series of lectures in June 2019 and whose observations and questions were very helpful. The two reviewers whose thorough work and detailed comments helped me significantly improve the manuscript. The proof-readers who improved my English. And of course the editors of the series Studies in Indo-European Languages and Linguistics, O. Hackstein and C. Melchert, for welcoming the book. Lastly, I owe special thanks to my students at Sorbonne Université, before whom I tested the hypotheses and arguments developed here: their reactions were probably the best touchstone I could get.