For non-native speakers of most languages, traps exist in relation to the use of words which appear, from their formal definitions, to be close synonyms. There are several different reasons for this.
One them is the fact that certain collocations tend to prevail over time, reflecting the fact that for various reasons (or with particular situations), speakers of that language have grown to prefer particular combinations over others. For example:
a) Who is your significant other? [a psychobabble term meaning "love interest/sexual partner/spouse, etc."]
is idiomatic, but
b) *Who is your important other?
Sometimes, completely different meanings can emerge from the use of what might seem to be almost exact synonyms. For instance:
i) That mountain is very close to us
ii) That mountain is very near to us
mean exactly the same thing. However, the adverbs derived from them do not; the sentences
iii) I'm closely following his progress [idiomatic]
iv) *I'm nearly following his progress [totally unidiomatic, with an unclear meaning]
are not at all similar in terms of the meanings they generate.
Another complication is that because word order is important in English, the position of a word in a sentence can have a significant effect on its meaning. For example:
1) Technique X largely contributed to the understanding of Y
means "Technique X's main contribution was in terms of the understanding of Y."
However, if we change the order slightly:
2) Technique X contributed largely to the understanding of Y
an ambiguity is introduced, because a slightly different additional meaning can be inferred:
"Technique X's contribution to the understanding of Y was significant."
Now let's take what many people might think of as a close synonym of 'largely' — greatly — and substitute that into sentences 1) and 2):
3) Technique X greatly contributed to the understanding of Y
4) Technique X contributed greatly to the understanding of Y
Here — for no particularly logical reason — unlike the case with 'largely', the meanings of these two sentences are exactly the same, namely
"Technique X made a very large contribution to the understanding of Y".
Unfortunately, as is probably apparent by now, these kinds of distinctions cannot be perceived using logic alone. They must be repeatedly encountered (preferably in a meaningful context) and learned.