Diachronic linguistics ('language history') distinguishes between two types of historical language contact (cf. <span class="bibl" data-bibl="krefeld2003">Krefeld 2003</span>), both of which have a geographic basis and are predicated on the language that was spoken in the area of interest during the period under study. This language is sometimes referred to as a 'strat': <li>Languages formerly spoken in the study area ('older strata') are referred to as 'substrates'. Over the course of history, these languages have been displaced by the language that is the focus of the respective language history: the strat </li> <li>Languages that entered the study area secondarily, as a result of conquest, and overshadowed the primary language for a certain period of time are referred to as 'superstrates'. However, these languages were not able to displace the overshadowed languages and disappeared – even after a more or less long period of time – for example in the wake of political change. That is why, for instance, the German superstrate of the Romance- and Slavic-speaking areas of Austria-Hungary perished with the disintegration of the state after the First World War.<br>
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Thus, one only speaks of <span class="vaabr" data-vaabr="sub">sub</span>- and superstrates from the perspective of a time in which the respective languages are no longer spoken in the area of study. Consequently, large time spans often have to be bridged so that contact-induced changes, meaning the results of language contact, can be detected based on the linguistic systems. However, for the genuine understanding of the presumed language contact phenomena, the historical period of the respective bilingualism is decisive, i.e., the time in which both languages were spoken in parallel or simultaneously. These concurrent languages are called 'adstrates'. However, a synchronic perspective that is not limited to the 'languages' but also takes into account the 'speaker' with his or her specific competence and possibly the concrete utterance, the 'speaking', must inevitably be adopted. Although this is often impossible from a historical perspective, it must technically be taken into account when reconstructing the stratigraphy because the utterance of a bilingual speaker differs fundamentally from that of a monolingual speaker.  <div id="krefeld2003" style="display: none;">Krefeld, Thomas (2003): Methodische Grundlagen der Strataforschung, Berlin/ New York, in: Ernst, Gerhard (Hrsg): Romanische Sprachgeschichte, DeGruyter, 555-568</div></li><div id="ABR_sub" style="display: none;">Substantiv</div>