Puro y simple isn’t so pure and simple!
In legal contexts puro/a (y simple) cannot generally be translated literally as “pure (and simple),” since the expression often means “unconditional.” Obligaciones puras (“unconditional obligations”) are those that are not subject to any condition or term (no sujetas a ningún tipo de condición, plazo o término) and, thus, payment or performance of those obligations may be demanded at any time. Donación pura y simple denotes an “unconditional gift,” in contrast to a donación modal (or) donación onerosa upon which the donor has imposed a condition or encumbrance.
With regard to negotiable instruments (títulos valores), checks and bills of exchange (cheques y letras de cambio) must contain an “unconditional order to pay a fixed amount of money.” In Spanish this is expressed as un mandato puro y simple de pagar una suma determinada. And in the context of the law of succession (Derecho de sucesiones) heredero puro y simple denotes an heir who accepts his inheritance unconditionally (known as aceptación pura y simple), without exercising the option to limit his liability for the debts of the inherited estate to the value of the inheritance (called beneficio de inventario).