The foundation theory of evidence requires well-founded evidence as its initial basis in order to create an effective inferential chain between the evidentiary fact and the fact of consequence. The fact of consequence is the essential element of the claim. Well-founded evidence means the evidence satisfied with the “foundation” requirement. To achieve this “foundation” requirement, the evidence must be case-specific, assertive and probably true. This requirement of “foundation” derives from the rule against speculation. “Speculation” is the inferential process of substituting generalizations for facts that are unsupported by evidence. Generalizations must be distinguished from evidence although they are inevitable in the inferential process of fact-finding. They should always be supported by evidence. The foundation theory of evidence requires well-founded evidence as the initial basis of the inferential chain in order to prevent speculation.