The material engagement approach, as I now think of it and as I was saying, part of that, comes from thinking about approaches to the material reality, which one can think about in terms of sculpture or in terms of the archaeological record. I also found that in trying to think about cognitive archaeology one came upon some related issues. I began to see that when we're laying great emphasis on symbols, Leslie White suggested that culture is man's material adaptation, and laid great emphasis on the use of symbols and, a, a symbol, if you define it is really where one thing represents another. X is a symbol representing Y, in context C. And so X is the signifier, if you like that terminology and Y is the thing signified. But I began to realise that the real innovations, if we're talking about the development of symbolic systems in the past. How humans began to create a more elaborate world, the real innovations weren't so much that this represents that, the signifier represents the thing signified, it was more the whole relationship that emerged. In my inaugural lecture in Cambridge in 1982, “Towards an Archaeology of Mind”, I'd spoke about those Indus Valley weights and how indeed it is the case that by looking at the weights and by measuring them, you become aware that there was a weighing system in operation which you can investigate, and that was for me, the beginning of some new thoughts in the field of cognitive archaeology. But when you ask yourself, okay, what do the weights actually represent? Well, this weight, if it weighs 50 grams, represents 50 grams. But, if you've never had a weighing system before, what exactly is going on? And, and the interesting question becomes, how does this come about? And how it clearly comes about is an experience in the material world that you've been walking on the beach or something and you've got this pebble and this pebble, and they seem to be about the same in some way. We, talking of weights and measure will say they're about the same weight, but you don't yet have a concept of weight and then at some point you notice that you can balance things and that you have a piece of wood and a pivot or whatever, then if they really feel that similar they will sit and balance. And then you realise, that if you take this stone away and get a different stone of a different colour maybe indeed of greater density, the smaller stone can still be the same weight as the larger one if this is, as we would say, of greater density and so the notion of weighing comes from a new experience of the world, which is the weightiness or matterness of these things, the degree to which they are heavy and so one begins to appreciate that the whole notion of weighing comes about through a new experience of the world, a new material engagement with the world. And so, it isn't a question of just assigning symbols, it's whole categories of relationships which have to develop, before they can be described, and so you really have to have the whole business of weighing coming about before X, the signifier will signify Y, in terms of a weight system.