 Bird (2007) has defended the epistemic definition of progress (accumulation of knowledge) against the semantic conception (accumulation of true beliefs or succession of theories with increasing verisimilitude). Here knowledge is not defined as justified true belief, but still it is taken to entail truth and justification, so that Bird’s epistemic view in fact returns to the old cumulative model of progress. According to Bird, an accidentally true or truthlike belief reached by irrational methods without any justification does not constitute progress. This kind of thought experiment may seem artificial, since there is always some sort of justification for any hypothetical theory which is accepted or at least seriously considered by the scientific community. But Bird’s argument raises the important question whether justification is merely instrumental for progress (Rowbottom, 2008) or necessary for progress (Bird, 2008). Another interesting question is whether the rejection of unfounded but accidentally true beliefs is regressive. The truthlikeness approach replies to these problems by distinguishing real progress RP and estimated progress EP: justification is not constitutive of progress in the sense of RP, but claims of real progress can be justified by appealing to expected verisimilitude (Cevolani and Tambolo, 2013). On the other hand, the notion of progress explicated by EP (or by the combination of RP and EP) is relative to evidence and justification but at the same time non-cumulative.