In this paper I claim that the bias to pass from the acknowledgement of the explanatory virtues of a hypothesis to the belief that it is true or approximate to the truth is so strong that scientific realists can hardly elude that temptation. For that reason, some philosophers, like McMullin and Okasha, following Peirce and Hanson, participate of the conviction that the skill of founding scientific explanations bears the ability of founding true theories. But, this way, they pass the limits that they themselves had fixed and their attempt to overcome objections like the one which was formulated by van Fraassen against the inference to the best explanation fails.