"Evidence-Indices [e.g., smoke as a sign of fire] may always have been used in an unthinking way by people going about their daily business; but to elevate them into being a reliable basis for theoretical knowledge..." -- David Wootton, The Invention of Science, p. 427
Here we come to the basis of Wootton's extraordinary claims about the Scientific Revolution replacing a world of abysmal ignorance with one that for the first time contains true knowledge: Wootton does not consider what ordinary people do in their day-to-day activities to be thought at all. But this is wrong: To move from an index to what that index signifies is an act of interpretation. In other words, it is thinking. It may not be great thinking, it may not be theorizing, and the move may have become so habitual that the thinker barely notices the thought involved at all. But nevertheless, it is an act of intelligence, and constitutes a genuine form of knowledge, without which the human species would not have survived a week after it had evolved.
Abstract thought does not have as its foundation "raw sensation" or any other such impossibility: its only possible basis is concrete thought.