The Indus Valley script doesn't look like a mere form of ornamentation to me (knowing something about archaeology and historical linguistics). The problem thou

The Indus Valley script doesn't look like a mere form of ornamentation to me (knowing something about archaeology and historical linguistics). The problem though is that when we say "writing" we usually mean "encoding otherwise spoken language in durable form" and there is no real evidence that this is what the Indus Valley script does. The problem is that there are plenty of kinds of markings that don't fall under either of these. Take for example Roman Numerals. You aren't encoding IX or VIIII as the word "nine" or equivalent in any language. Instead You are illustrating the number on a tally stick and the tally stick, rather than the spoken language, acts as the shared point of reference. So I think one has to be careful about saying that these are the only two options. The script could have a communicative function and even a formally defined one (much like Roman Numerals do) without being writing in the sense of encoding spoken language in durable form.