word". Meillet showed that what was at issue was not the origins of grammatical forms but their transformations. He was thus able to present a notion of the creation of grammatical forms as a legitimate study for linguistics. Later studies in the field have further developed and altered Meillet's ideas and have introduced many other examples of grammaticalization. During the second half of the twentieth century, the field of linguistics was strongly concerned with synchronic studies of language change, with less emphasis on historical approaches such as grammaticalization. It did however, mostly in Indo-European studies, remain an instrument for explaining language change. It was not until the 1970s, with the growth of interest in discourse analysis and linguistic universals, that the interest for grammaticalization in linguistic studies began to grow again. A greatly influential work in the domain was 's Thoughts on Grammaticalization (1982). This was the first work to emphasize the continuity of research from the earliest period to the present, and it provided a survey of the major work in the field. Lehmann also invented a set of 'parameters', a method along which grammaticality could be measured both synchronically and diachronically. Another important work was Heine and 's Grammaticalization and Reanalysis in African Languages (1984). This work focussed on African languages synchronically from the point of view of grammaticalization. They saw grammaticalization as an important tool for describing the workings of languages and their universal aspects and it provided an exhaustive list of the pathways of grammaticalization. The great number of studies on grammaticalization in the last decade (up to 2018) show grammaticalization remains a popular item and is regarded as an important field within linguistic studies in general. Among recent publications there is a wide range of descriptive studies trying to come up with umbrella definitions and exhaustive lists, while others tend to focus more on its nature and significance, questioning the opportunities and boundaries of grammaticalization. An important and popular topic which is still debated is the question of unidirectionality. Mechanisms It is difficult to capture the term "grammaticalization" in one clear definition (see the 'various views on grammaticalization' section below). However, there are some processes that are often linked to grammaticalization. These are semantic bleaching, morphological reduction, phonetic erosion, and obligatorification. Semantic bleaching Semantic bleaching, or desemanticization, has been seen from early on as a characteristic of grammaticalization. It can be described as the loss