Ineffability is concerned with ideas that cannot or should not be expressed in spoken words (or language in general), often being in the form of a taboo or incomprehensible term. This property is commonly associated with philosophy, aspects of existence, and similar concepts that are inherently "too great", complex, or abstract to be adequately communicated. In addition, illogical statements, principles, reasons, and arguments may be considered intrinsically ineffable along with impossibilities, contradictions, and paradoxes. Terminology describing the nature of experience cannot be properly conveyed in dualisticsymbolic language; it is believed that this knowledge is only held by the individual from which it originates. Profanity and vulgarisms can easily and clearly be stated, but by those who believe they should not be said, they are considered ineffable. Thus, one method of describing something that is ineffable is by using apophasis, i.e. describing what it is not, rather than what it is. The architect Le Corbusier described his design for the interior of the Chapel of Notre Dame du Haut at Ronchamp as "l'espace indicible" translated to mean 'ineffable space', a spiritual experience which was difficult to describe.
"Tao can be told but any definition given is not perpetual; the name can be named but whatever name given is not perpetual." — Chapter One, Tao Te Ching
"My life, the most truthful one, is unrecognizable, extremely interior, and there is no single word that gives it meaning." — Clarice Lispector
T.S. Eliot's poem "The Naming of Cats" (1939) playfully suggests that every household cat must bear (besides whatever the family calls him) two additional names: one an exotic appellation shared by no other cat; the other forever unutterable because it is known only to the cat himself ("His ineffable effable / Effanineffable / Deep and inscrutable singular Name"). This idea is carried on in the movie "Logan's Run".
"Moses said to God, 'Suppose I go to the Israelites and say to them, "The God of your fathers has sent me to you," and they ask me, ‘What is his name?’ Then what shall I tell them?” God said to Moses, “I AM THAT I AM" — Exodus 3:13-14 (New International Version) (see Tetragrammaton).
The nature of qualia (sensory experiences), such as colors or flavors (Although this has been challenged recently by research on ideasthesia finding that qualia are connected in semantic-like networks.)
The nature of emotions (with love being a prominent example)