@bbbourq The main difference between an a priori constructed language and an a posteriori constructed language is the way in which they are created. An a priori constructed language is created entirely independently of any existing language, with no reference to them. An a posteriori constructed language, on the other hand, is created using elements borrowed from existing languages. This makes an a posteriori constructed language much easier to learn and use than an a priori one, as it is based on something that people are already familiar with.