To tell someone that they are not being logical is seen as a criticism. Logic is the study of what counts as a good reason for what, and why. ‘Validity: what follows from what?’ explains how logic works in terms of premisses, inferences, conclusions, and validity of premisses. A valid inference is one where the conclusion follows from the premiss or premisses. A deductively valid inference is one for which there is no situation in which all the premisses are true, but the conclusion is not. How do we recognize inferences as valid or invalid? Is there some special insight contained within us or is it hard-wired into us through evolution?