Small comma, big difference

One of my students from my tuition class told me she thought something was wrong with the example below, but couldn't quite figure out why:

Conquer Synthesis & Transformation, 2009

She was right. It's unfortunate that the example on the use of whose at the beginning of the synthesis exercise had a mistake.

The relative clause whose project is due next Monday should have been set off by commas.

Without the commas, the relative clause is restrictive. Restrictive clauses define or restrict the noun they modify. However, Steven is a proper name and proper names have a specific reference and do not need further defining.

The sentence should have been written as follows:

(1) Steven, whose project is due next Monday, has fallen ill.

With the commas, the relative clause becomes non-restrictive and merely adds non-defining information to the proper noun Steven.

The restrictive version would be correct if we wanted to refer to a certain Steven. To do this, we use the definite article the:

(2) The Steven whose project is due next Monday has fallen ill.

Sentence (2) refers to a particular Steven, and the restrictive clause serves to pick out that specific individual.