Olivier Messiaen developed his basic sign system in the 1930s and 40s and expanded it in the 1950s and 60s. In 1969 he was again looking for a solution to the problem of a 'musical language that can be communicated'. Various aspects of numerology have also been used in musical cryptography for their symbolic value. Arthur Honegger's cipher uncovers several important problems inherent in encrypting words in music. The French tradition of musical cryptography continued well into the second half of the twentieth century. The Deuxieme symphonie is also of interest because of the possible correspondence between Langlais's use of the words 'God' and 'Mary' and Messiaen's concept of the leitmotifs – one of the leitmotifs in the Meditations is also 'God'. Messiaen explains some of the basic compositional procedures for the cryptography of his langage in the preface to the score of the Meditations.