You must understand both the writing system and the language(s) in order to claim a decipherment. Most successful decipherments are based on bilingual or trilingual inscriptions (e.g. cuneiform, Egyptian hieroglyphs, and the Cypriot Syllabary) or knowledge of the underlying language(s) (e.g. Linear B and Maya hieroglyphs). In cases where one has neither, such as Linear A, Cypro-Minoan, and the Indus script, decipherment may prove impossible.

Linear B has been deciphered successfully because the language was identified (Mycenaean Greek), and scholars were able to understand words based on their knowledge of Greek. For example, a-ku-ro corresponds to Greek ἄργυρος ("silver") and pa-te is instantly recognizable as Greek πατήρ ("father").

The language of Linear A, however, has not yet been identified, and the grammar and lexicon therefore remains elusive. It's as if someone who speaks French picked up a book written in Hungarian. Since Hungarian uses a modified version of the Latin alphabet, the French speaker would understand the letters of each word and perhaps even be able to read them out loud more or less accurately. The meaning of the text, however, would be incomprehensible without learning Hungarian.