I have a question regarding quantization. In most cases one never starts with a quantum theory, but always writes down a classical expression, goes through quantization, implementation of constraints (Dirac, BRST, ...), construction of Hilbert space, inner product, measure of an path integral etc. to arrive at a viable quantum theory. Hopefully the theory is anomaly free, finite / renormalizable etc. I would like to question this approach which is based on the classical limit and constructs a quantum theory via ad-hoc rules. It's like starting with a drawing and derive from it how the final building shall look like; w/o having ever seen a building, experience as an architect or with construnction this will never work. So my question is if there is another approach, a research program, ..., to write down or "construct" quantum theories w/o using classical expressions as a starting point?