In this article we present some of the problems connected with the formation of the First Czechoslovak Republic from the legal point of view. Our aim is to point out that the First Czechoslovak Republic could not arise for the Slovaks on the 28th of October, 1918. Our argumentation is firstly based on the historical discussion (descriptive level) which was held in the past, but at the same time we try to formulate conclusions applicable on other similar cases within nowadays discussion (prescriptive level). In the beginning of the article we analyse the thesis according to which the First Czechoslovak Republic was created on the 28th of October, 1918, while trying to come to terms with the arguments that support this legal fiction. Consequently we analyze the thesis that the First Czechoslovak Republic could not be legally created for the Slovaks on the 28th of October, 1918, because at that time the Czechoslovak Republic did not execute its effective power on the Slovak territory. To support this thesis we use also the stable practice of the Supreme Administration Court. At the end of the article, we try to summarize all the previous arguments and draw the attention to the lack of explanatory power of the legal fiction claiming that the Czechoslovak Republic was created on the 28th of October, 1918.