  The Turing machine is ‘theoretical,’ in the sense that it is not intended actually to be engineered (there being no point in doing so), although it is essential that its atomic components (the paper tape, movement to left and right, testing for the presence of a symbol) are such as could actually be implemented. The whole point of the formalism is to reduce the concept of ‘method’ to simple operations that can unquestionably be ‘effected.’