A thesaurus can be a very useful tool for non-native speakers, but it can also be quite problematic. It is generally good to use a variety of words as it shows you have a wide vocabulary. A thesaurus can give you a great variety of synonyms to use, but make sure before you pick up your thesaurus, you know how to use it properly.
Firstly, make sure you know that the meaning of the synonym you have found is the same.
It must be remembered that words can have more than one meaning; take for example row. This word can mean line or argument. So for example, you cannot replace “There was a row within the government about the spending cuts” with “There was a line in the government about the spending cuts.” This sentence just doesn’t make sense! There are also more subtle differences in meanings between words, but they are no less important. You must always be sure the synonym works in context.
Secondly, make sure the level of formality is the same.
A synonym of angry is worked up. Yet, worked up is an informal way of saying angry. Whereas you could use angry in a more formal piece of writing (“The minister was said to be angry about the policy reviews”), if you replaced angry with worked up, your writing would become less formal. Some words can also be overly formal.
Thirdly, the frequency of the synonym is important to remember.
Take, for example, the following sentence; “There are many arguments regarding taxation in the UK”. If you wish to use a synonym for argument, you can find the word quarrel. The meaning is the same, the formality is roughly the same. However, this word can seem a little unnatural to some native English speakers (it can seem old-fashioned).
If you want to use a synonym, try to use a word you already know, or use a learner’s thesaurus which is especially designed for non-native speakers. A more general thesaurus is a tool to help remind you of words you already know, not a tool for learning new words. So, beware the dangers and use them with care!