In January, Brooklyn teenager Osiris Aristy was arrested for “making a terroristic threat”. If convicted, this would carry a sentence of up to seven years in prison. In part, the case turns on the use of emojis in some of the 17-year-old’s Facebook status updates. Among other posts, expressing typically teenage concerns, three now-deleted updates appeared to convey his disdain for the police using emojis of a police officer and a revolver.

This case is especially noteworthy as the basis for Aristy’s alleged “terrorist threat” – which falls under the New York legal statutes on terrorism (introduced after 9/11) – does not include a written or verbal threat. Aristy’s arrest was primarily based on his use of emojis.

Emojis originated in Japan. They literally mean “picture”(e)-”character” (moji). As you might expect, emojis are particularly popular among teenagers, where they can be used as a shorthand symbol to express an often fairly complex idea or emotion in a visually evocative and appealing way. But can emojis be construed as a language; one that can potentially fall foul of increasingly stringent anti-terrorist laws around the globe?

Emojis constitute a class of what linguists refer to as icons. Like the recycle bin or trash can on your computer desktop, an icon is a sign that, in some way, resembles the thing it evokes. The recycle bin icon on my computer is the place where I delete files. But in most cases, natural languages such as English or Japanese eschew icons in favour of signs known as symbols, which are quite different from icons. The symbols (or words) that make up a spoken language are meaningful, not because of any inherent resemblance relationship with the ideas that they point to, but rather, their meaning derives from an unspoken agreement between speakers of a linguistic community: the symbol will point to a specific entity or idea, agreed upon by all. This is known as a “linguistic convention”. For instance, the same idea conveyed by the English word “cat” is represented in different ways, across languages: “chat” in French, “billi” in Hindi, and “ikati” in Zulu, for instance.

So, from this perspective, emojis – icons – function in quite a different way from the symbols used in English. Nevertheless, spoken languages do make use of some iconic signs. Many English words for animal sounds, ranging from “buzz” to “moo”, are iconic: they resemble the sound produced by the animal they relate to, the bee and the cow respectively. And English is not unusual in this.

But language is not restricted to a specific medium for its expression. Since the 1960s, it has been recognised that sign languages, which make use of the manual-gestural medium, are fully functional languages, with the same levels of lexical and grammatical complexity as spoken languages. And as findings on signing have amassed, today we know that sign languages make extensive use of iconic reference, arguably far greater than in spoken languages. This is a consequence of the medium of expression: hand shapes and gestures can more readily depict an idea or entity, in iconic fashion, than is possible in the spoken medium. This shows that the once-heralded hallmark of human language – that it predominantly makes use of symbolic reference – may not be a hard-and-fast requirement for a communicative system. As emojis amount to iconic signs, ideally suited to the visual medium of expression, they are not automatically disqualified from being language-like.

Perhaps a better way of characterising a language, then, is in terms of the functions it fulfils. There are two very important ones: first, a language is used to convey ideas, and, second, to influence others. In short, an important function of language is to enable us perform actions, sometimes referred to as “speech acts”, that can even change aspects of the world. These might range from the significant, when a member of the clergy pronounces a couple husband and wife, to the more banal, as when I ask a passerby in the street to give me the time. And from this perspective, the use of emojis, potentially at least, can be used to fulfil both functions: they can convey ideas, and be used to influence the mental states, emotions, and even behaviours of others.

In the case of Osiris Aristy, the issue will turn on whether a reasonable person would interpret his teenage disdain as a terrorist threat; or perhaps, whether his use of emojis was intended as a threat. And that is a slightly different issue. But, as emojis, and the way they are increasingly being used, share some of the attributes common to language, then, in principle at least, they could be used to make terrorist threats, and can be interpreted as such.