By selecting the related (cognate) words, children begin to engage in elementary school. However, older students and philology students are selected related words with caution. Why?
Related words - words (tokens) that have the same root, but relating to different parts of speech (white - white - to turn white). To find the root word, not necessarily a good thing to know the derivation, the more that the basic information on this topic Russian language taught in elementary school. However, it is useful to remember that the difference related words is a particular set of suffixes (prefixes) and suffixes (suffixes only). The words have the same root, but differ only inflections (endings), related words are not, it is a form of the same words, and the rivers, in the rivers. In the Russian language there are several most common ways of word formation: prefixing (only the prefix is added), suffix (suffix only) prefixal-suffix (prefix and suffix). But to form a cognate (related) words prefixing the method is not suitable strongly. Indeed, in this respect, there is a big difference, for example, in the words: run, run in, run-in, etc. It must be remembered and on the homonymous roots. So, the word water-Yana and water-it will not be related, since the roots of the values in this case are different. In addition, the Russian language there is such a thing as conversives. The simplest example: "he has won - you have lost," in which the word "won" and "lost" are precisely conversives, words expressing the same effect, but in opposite directions. Here at the forefront the semantics of the word in context. So if you, for example, offer to find the root word in the sentence: "Karpov, Kasparov wanted to win, but Kasparov has not succumbed to it and did not lose," think before giving a definitive answer.