symbolic, the iconic, the indexical. It's not a binary: signs differ in how arbitrary they are. And they are niot exclusive types but Three Modes of Relativity. 43 So, Chandler makes notes on the symbolic, the iconic, the indexical 36-7 - with three degrees of conventionality and motivation: "the terms 'motivation' (from S) and 'constraint' are sometimes used to describe the extent to which the signified determines the signifier. The more a signifier is constrained by the signified, the more 'motivated' the sign is: iconic signs are highly motivated; symbolic signs are unmotivated. The less motivated the sign, the more learning of an agreed convention is required." 38
As modes, "whether a sign is symbolic, iconic, or indexical depends primarily on the way the sign is used" via T Hawkes, 43. "Signs cannot be classified ... w/o reference to the purposes of their users within particular contexts." 43
We can have historical shifts in signs, contextual influences and changes (from B&W to color photos, from analogue to digital reproduction) ... Chandler 44 ff. Issue is a matter of evolution, development, a moment from motivation to arbitrarity/convention, depending on whether we assign one mode as primary.