This article series aims to eliminate usage errors and help non-native speakers to write clearly and fluently. We suggest that you always do proper research and use style guides effectively. For anything you are not sure of, feel free to ask us.
improve, increase, bolster, boost, develop.
“Deepen” is a difficult word to use correctly. In addition to its literal meaning (e.g., deepen a well), it can also be used figuratively to mean “to increase,” “improve” or “boost.” However, it cannot be used indiscriminately in this way and can actually only be associated with a few abstract terms like “knowledge” or “understanding.” It can also never be used to mean “look into something more deeply,” as in “deepen an issue.”
“The extension of SJU would enable stakeholders to
deepen strategic partnerships.”
Misused English words and expressions in EU publications by Jeremy Gardner [Updated 8.11.2013]