Using quantifier-floating as an example, I have argued that natural language is a well-behaved object of empirical science. That is, (i) grammaticality reaction has high degree of reproducibility, (ii) a working hypothesis makes a prediction, and (iii) the hypothesis is either falsified or verified. The mutual c-command condition on floating quantifiers is another manifestation of economy in natural language. I proposed that the unambiguous path condition on phrase structure is deducible from the law of entropy. Self-reproduction (trace/copy production) in natural language conforms to the general formula for self-reproduction in inorganic systems: A+X→2X+(B). It remains a mystery why natural language, which has emerged in the organic system of the human brain, exhibits properties of the inorganic world such as economy, entropy, and self-reproduction.