There are various synonyms that can be used for the phrase "tell/see the difference". One of the most popular is "discern", which refers to the ability to recognize subtle distinctions between two or more things. Other synonyms for this phrase include "distinguish", "differentiate", "contrast", "compare", and "separate". Each of these words has a slightly different connotation, which may be more or less appropriate depending on the context in which they are used. For example, "contrast" may be the best choice when comparing two things that are very similar but have some key differences, while "compare" may be more appropriate for highlighting similarities between two distinct items.