What the four words mean

A certificate is short and narrow — weeks to a year — and teaches one skill set. A diploma is longer, usually one to two years, vocational in shape, and aimed at getting you working. A bachelor degree is three or four years and is the credential most professions treat as the baseline. A postgraduate degree assumes you already hold the baseline.

These are not four rungs of the same ladder. A diploma is not a shorter degree; it is a different product with a different buyer. Confusing the two is the single most expensive misunderstanding we see.