You do not necessarily have to train in a skill in order to use it; Argo calculates defualt skills levels. Four dice are rolled, rather than the normal three, and any amount by which the skill's Intelligence rating exceeds yours is subtracted from the roll. Special class skills — spells and psionic abilities — cannot be rolled as defaults: you have to know the skill. In addition, the staff can define specific skills in such a way that they may not be rolled at default levels.

You may attempt to use a skill you do not know — provided that it can be rolled as a default — but your chances of success are much lower. When you roll against a skill you do not know, four dice are rolled against the base, minus the amount by which the skill's Intelligence rating exceeds your Intelligence. So, if Denali, INT 12, does not know the Engineering skill (Intelligence rating 14), he could nonetheless attempt to design a jury-rigged component to repair his starship's life support system: he would succeed if he rolled 10 or less (INT 12 - (IR 14 - INT 12) = 10) on four six-sided dice. (Actually making the component would require a separate roll against his Mechanic skill.)

Although the programs will allow a roll for non-special class default skill, players and Monitors should exercise realistic restraint. If Corell is a barbarian from the Outworlds, with virtually no exposure to technology, he should not be allowed a default roll to reprogram the starship's security system.