A few theories as to the 'birth' of the name currently exist.

"The theory of a marginal performer doesn't exist in our company."

Various theories exist regarding the origin of the name itself.

A real theory exists only when the laws of force are given.

No evidence has come to light to prove a conspiracy, although several theories do exist.

The origin of the name is unknown, although several theories exist.

Various theories as to the origin of the name exist.

The truth is that no one really knows how the name came about, although several stories and theories exist.

No theory exists, or was offered, to explain the blue light.

Several theories exist as to why the card is so rare.