I encounter it in many books as well as web. Natural Language Processing and Machine Learning are said to be different subsets of Artificial Intelligence. Why is it? We can achieve results of Natural Language Processing by feeding sound patterns to Machine Learning algorithms. Then, what’s the difference?
Because they are different: One does not include the other.
Yes modern NLP (Natural Language Processing) does make use of a lot of ML (Machine Learning), but that is just one group of techniques in the arsenal. For example, graph theory and search algorithms are also used a lot. As is simple text processing (Regular Expressions). Note I also said “modern NLP” – the statistical approach to NLP is a relatively recent development over the past few decades. I understand a more formal approach (e.g. based on parsing formal grammars) was the norm back in the 1960s/1970s.
Similarly ML does not have to use NLP, and usually it doesn’t, although some applications might use NLP techniques (eg. to process text input).