Florentin Smarandache
2000
This representation is closer to the human mind reasoning. It characterizes/ catches the imprecision of knowledge or linguistic inexactitude received by various observers (that's why T, I, F are subsets - not necessarily single-clements), Uncertainty due to incomplete knowledge or acquisition errors or stochasticity (that's why the subset I exists), and vagueness due to lack of clear contours or limits (that's why T, I, Fare subsets and I exists; in particular for the appurtenance to the neutrosophic sets).
Read this work at the World Public Library (library card needed).