One of the most important feature of Shannon's theory was the concept of entropy, which he demonstrated to be equivalent to a shortage in the information content in a message. According to the second law of thermodynamics, as in the 19th century, entropy is the degree of randomness in any system always increased. Thus many sentences could be significantly shortened without losing their meaning. Shannon proved that in a noisy conversation, signal could always be send without distortion. If the message is encoded in such a way that it is self-checking, signals will be received with the same accuracy as if there were no interference on the line. A language, for example, has a built in error-correcting code.