It is possible to produce something that is grammatical either by chance or under the supervision of another. To be proficient in grammar, then, one must both produce what is grammatical and produce it grammatically, that is, in accord with knowledge of grammar in oneself.

Descartes's epistemology is a special case of Aristotle's virtue ethics.

Arguably, if you view a real barn in bright sunlight and close by, while fully alert and otherwise in good shape, then you do know whether or not you see a barn. You have "animal" knowledge, says my virtue theory, through the first-order aptness of your judgment.

A successful account enables us to understand human knowledge in general.

Lowered reliability obviously yields a lesser competence. But lowered breadth does so as well.

You attain aptness by judging while in good shape and in a good situation (good light, good distance, etc.), through the exercise of good barn-sorting epistemic competence.

One does not avoid incompetence if one makes an attempt whose likelihood of success is too low. This seems little more than analytic: when the performance is in a domain that imposes standards of risk, attempts may or may not meet such standards. And the relevant competence of agents then includes reliably enough meeting those standards.