The president's son was named John F. Kennedy, Jr.
Wrong: The president's son was named John F. Kennedy, Jr.
Why: The name suffix "Jr." is preceded by a comma.
Right: The president's son was named John F. Kennedy Jr.
Why: While suffixes like "Jr.," "Sr." and "III" have traditionally been preceded by commas, and some still see this as a gray area, the majority of grammarians now agree the commas shouldn't be there. When an identifying word or phrase has a comma before it, it typically means that word or phrase can be removed without changing the meaning. In the case of these name suffixes, removal results in a different meaning altogether. As such, these essential suffixes are not preceded by commas.
Degree suffixes, on the other hand, like "M.D.," "Ph.D." and "B.A.," do typically take preceding commas.
Next, we'll head further into the essential/nonessential zone …