First of all, it is important to understand that each word has a particular form, i.e. a certain combination of features. On these grounds, which may be reflected, for example, in the ending (inflection), it is possible to effortlessly identify the part of speech. For example, only verbs have endings "et", "it", "at", "Yat", and only the participle suffix "usch", "yusch", "arg", "crate".

To form words are different grammatical characteristics of certain parts of speech. For example, you can determine the verb form, time, person, number, conjugation, transitivity. But in the grammatical form of the noun is enclosed signs of number, case, declension, kind. So, in the sentence "Guys, love and take care of our language the word "language" is used in the form of the accusative, singular.

Form of the word can change. For example, in the sentence "Prepare the abstract about the importance of our language the word "language" is already used in the form of the genitive, singular.

However, in the Russian language there are words in which the form of the word remains the same forever. They are called immutable parts of speech. They can not identify any category of person, number, case, etc. such words are adverbs (fast, far, often, etc.), gerunds (seeing, looking, touching, etc.). They have no end, even zero, since the ending is part of the changed words.

Unfortunately, errors occur frequently in identifying words with the same form and cognate words. Probably this can be explained by the fact that in both cases, the words will be one and the same root. However, by changing the form of words, you will be changing only his end, but all the remaining morphemes (prefixes, suffixes), included in the framework will remain unchanged. For example, in the chain of word "pilot pilot pilot" part of each word includes the root of "years" and the suffix "Chik". Therefore, these forms of the same word.

If we compare the words "water - underwater - submarine", it is possible to detect some differences in the composition of words. Despite the fact that all words have the same root "water", the foundations have different. The word "water", apart from the root "water", the basics - the suffix "n" in the word "underwater" - the prefix "under" and the suffix "n" and released the "submariner" - the prefix "under" and the suffix "Nik". Therefore, they are not forms of the same word. These words are related.