General Synonyms:
* Differentiate
* Discern
* Recognize
* Identify
* Tell apart
* Separate
* Set apart
* Characterize
More Formal Synonyms:
* Elucidate
* Ascertain
* Discriminate
Informal Synonyms:
* Spot
* Pick out
* Tell the difference
The best synonym to use will depend on the specific context of your sentence. For example, "differentiate" might be a better choice than "distinguish" if you are talking about the differences between two things.