720: In- Nov 27, 2016

'Irrational', 'illegal', 'impossible' and 'inhumane', morphologically speaking, have the same prefix, even though the initial 2 letters each are different. They all take the Latinate, 'in-' prefix which negates a word. To be sure, this is not the same as the 'in-' in 'import' and some other words that come from the preposition, or otherwise 'illegal' and 'impossible' would refer to something within the restrictions of the law or the realm of possibility, and that's quite the opposite of the truth. Certain phonemes are difficult to pronounce together—which is why most of the time, for example, the in in 'con-' will become an M such as in 'computer'—but other time the will remain the same like the N in 'inhumane'.