La liaison in French is a complex subject, with lists of when liaison is required, when it is forbidden and all the many possibilities when it is optional. (les liaisons obligatoires, les liaisons inerdites, and les liaisons facultatives)
Liaison is not technically a subject of pronunciation; it is a subject of when you must make it and when you must not. It is a case of learning (memorizing) all the cases when it is required or not. To simplify the subject, I am proposing here that the student do all the liaisons obligatoires, and for any other possibility, just don't make it. This path will guarantee that you will always be correct. There may be times when a liaison would have been o.k. But if you treat all other cases as “don't make these”you will never be wrong. So, if the case is not listed here, and you question whether to make a liaison or not, the answer is No don't make it; That way you will be guaranteed to not make a mistake in this subject.
Liaison is partly due to the grammatical closeness of the 2 words in question. So an article and its noun, or an adjective and its noun or a subject pronoun and its verb, are closely connected and therefore become a required liaison.
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