The reason: certain letters had been pulled from his packet.

Are there certain letters that occur more often than others?

Andrew would pick certain letters and go to visit them.

It is based on certain letters which are given values as numerals.

"I am off to Paris, when you shall have given me a certain letter."

At the elections each party has a certain letter, which is also used on posters for the campaigns.

The new words can be used to express a superstition about certain letters or numbers.

He brought out certain letters and laid them to one side.

Although ten, he cannot draw and writes certain letters backwards.

The alphabet was running through again, certain letters emphasized by longer space between them this time.