Alfred Marshall’s approach to economics hides a paradox. On one hand, the ‘father’ of neoclassical economics strongly favoured conducting economics as a positive science. However, the fact that Marshall was such a consistent and determined advocate of this ideal of economic research is puzzling for at least two reasons. Firstly, even a quick glance at his publications allows to notice that his texts are sated with moral teachings. What is more, in referring to the problems of economic policy he not only took into account ethical aspects, but also frequently gave pre-eminence to ethical arguments over conclusions stemming from research grounded solely on the theory of economics. The paper aims to explain the paradox and argues that the complexity of Marshall’s approach arises from his attempts to combine two approaches pointed by Amartya Sen of binding economics and ethics over the centuries: ‘the ethics-related tradition’ with ‘the engineering approach’.