We found a minimal and a comprehensive set of directly measurable quantities defining the most general Two-Higgs-Doublet Model (2HDM), we call these quantities observables. The parameters of potential of the model are expressed explicitly via these observables (plus non-physical parameters similar gauge parameters). The model with arbitrary values of these observables can in principle be realized (up to general enough limitations). Our results open the door for the study of Higgs models in

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... of measurable quantities only. The experimental limitations can be implemented here directly, without complex, often model-dependent, analysis of the Lagrangian coefficients. The principal opportunity to determine all parameters of 2HDM from the (future) data meets strong practical limitation. In the best case it is the problem for very long time. Apart from this construction per se, we also obtain some by-products. Among them -a simple criterium for CP conservation in the 2HDM, a new sum rules for Higgs couplings, a clear possibility of the coexistence of relatively light Higgses with the strong interaction in the Higgs sector and a simple expression for the triple Higgs vertex g(hahaha), useful for the analysis of future hhh coupling measurements. 1 In the analysis of data the parameters of Higgs Lagrangian are being obtained by a solution of complex enough set of equations. The problem of completeness, or predetermination of the observations that are necessary for complete description of the potential is usually not discussed.