A stepping stone is an action that helps one to make progress towards a goal. This definition, from the COD, includes the metaphorical goal. Although the etymology of goal (according to the OED) is “difficult,” it is indisputably a sporting term, first recorded in 1531. Its literal synonyms are aim or objective. In 2014, nearly 100000 articles contained the word aim (or aims), over 122000 objective (I did not check for use as the opposite of subjective), but only 18000 contained goal or goals. All three words appear as sub-heading words in abstracts, and sometimes the sub-heading is “aims and objectives,” which is tautologous.

A stepping stone is more than just a step: you can take steps as large or small as you like, and usually as quickly or slowly as you want. But to move from one stepping stone to another is to move a discrete distance, and sometimes an uncomfortably large one that requires good balance and the need to keep moving.

Few of PubMed’s® stepping stones are more than steps, and some of them would be better described as routes. “A temporary job can either be a stepping stone or a dead-end” is a good description. Such a job entails a discrete move and may be a poor one, but most biomedical research is by painstaking small advances, and most chronic diseases develop slowly. So it is inappropriate to describe a potent antibiotic derivative as a stepping stone towards the clinical development of that class of drug, or higher insulin secretion and insulin resistance – necessary though they might be – as the stepping stone to diabetes. Stepping stones are especially inappropriate in most discussions of evolution, a common application of the metaphor: “the orb was a stepping stone to the evolution of new web types” and “a plausible evolutionary stepping stone towards speech” misrepresent the mutation by mutation modification of the phenotype. Stepping stone doesn’t appear in The Origin of Species, although step or steps appears 34 times.

Stumbling block is just a clumsy synonym for obstacle. As Wiktionary puts it, “Idioms are a common stumbling block for learners of a language.” All the stumbling blocks that I found in PubMed® would have been better replaced. In the Old and New Testaments, a stumbling block is a behaviour or attitude that leads another to sin: I couldn’t find any of those in PubMed® either. The Greek word (rendered from the original Hebrew) is the root of scandal: of which there is plenty in PubMed®, both in descriptions of failures of service and in fraudulent research.

Neville Goodman is a retired consultant anaesthetist and a writer. He is co-author of a book on medical English.

Competing interests: I have read and understood BMJ policy on declaration of interests and declare that my only competing interest is my co-authorship of a book about medical English.