 Here Turing is emphasizing that the term ‘systematic method’ is not exact, and so in that respect is like the term ‘vegetable’ but unlike mathematically precise terms, such as ‘λ-definable’, ‘Turing-machine computable’, and ‘substitution-puzzle’. Hence his claim that the appropriate way to support a statement that pairs systematic methods with items falling under a mathematically precise description is to offer ‘propaganda’, rather than to attempt to prove it.