Single grammatical words have a fixed internal structure; when the structure is changed, the meaning of the word also changes. In Dyirbal, which can use many derivational affixes with its nouns, there are the dual suffix -jarran and the suffix -gabun meaning "another". With the noun yibi they can be arranged into yibi-jarran-gabun ("another two women") or yibi-gabun-jarran ("two other women") but changing the suffix order also changes their meaning. Speakers of a language also usually associate a specific meaning with a word and not a single morpheme. For example, when asked to talk about untruthfulness they rarely focus on the meaning of morphemes such as -th or -ness. Semantics Leonard Bloomfield introduced the concept of "Minimal Free Forms" in 1928. Words are thought of as the smallest meaningful unit of speech that can stand by themselves. This correlates phonemes (units of sound) to lexemes (units of meaning). However, some written words are not minimal free forms as they make no sense by themselves (for example, the and of). Some semanticists have put forward a theory of so-called semantic primitives or semantic primes, indefinable words representing fundamental concepts that are intuitively meaningful. According to this theory, semantic primes serve as the basis for describing the meaning, without circularity, of other words and their associated conceptual denotations. Features In the Minimalist school of theoretical syntax, words (also called lexical items in the literature) are construed as "bundles" of linguistic features that are united into a structure with form and meaning. For example, the word "koalas" has semantic features (it denotes real-world objects, koalas), category features (it is a noun), number features (it is plural and must agree with verbs, pronouns, and demonstratives in its domain), phonological features (it is pronounced a certain way), etc. Orthography In languages with a literary tradition, the question of what is considered a single word is influenced by orthography. Word separators, typically spaces and punctuation marks are common in modern orthography of languages using alphabetic scripts, but these are a relatively modern development in the history of writing. In character encoding, word segmentation depends on which characters are defined as word dividers. In English orthography, compound expressions may contain spaces. For example, ice cream, air raid shelter and get up each are generally considered to consist of more than one word (as each of the components are free forms, with the possible exception of get), and