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A state of rest is indistinguishable from a state of relative uniform motion. That’s relativity. A state of inertial acceleration is distinguishable from a state of rest and/or uniform motion by, to use Fred’s example, the introduction of a spring between a body and a force. A gravitational acceleration is distinguishable from an inertial acceleration by, for example, observing an electrically neutral test body in a container; it will distinctly express a situation as exclusively gravitational or inertial by either floating freely or tending toward one wall of the container. An exclusively inertial acceleration is distinguishable from an interrupted gravitational acceleration by “dropping” two objects; if gravitation is involved they will, if the measuring apparatus is sensitive enough, be observed to converge. All these latter cases are manifestly, self-evidently NOT relativistic. Please dispense with the condescension and either refute the concrete principles involved (without resorting to abstract, un-provable principles like “equivalence”) or accept them, and begin considering the implications.