Cross class & untrained skills

[morpheous1777]

Forgive me if this seems like a stupid question, but what are the rules for using cross class and untrained skills ?? I have read the PH but a fellow player said that a PC could put ranks in cross class untrained skills (alchemy, disable device, handle animal, innuendo, intuit direction, knowledge (all), pick pocket, profesion, read lips, spellcraft, and tumble) is this true ?? can a fighter put ranks in tumble then use it ?? By what i understand you cannot use untrained skills in any way (unless you have a feat, or ability that says you can).

 

[Mustrum_Ridcully]

Look in the Player's Handbook, in the chapter "Skills".

Each Skill has mentioned if you can use it untrained, or if you can buy it as a cross class skill (skills you can't buy this way are EXCLUSIVE, like Use Magic Device). A Fighter can buy ranks in Tumble, 2 skill points for each rank.

I believe (my books are downstairs, and I am a lazy guy), Alchemy, Disable Device, Intuit Direction, Scry and animal empathy can only be used trained. (this list is not complete)

Be aware that you can make some skill checks even if the skill is a cross class skill and exclusive (Scry, as an example).

You can make "untrainend" Knowledge Checks, but you can never know more than common knowledge, regardless of the check result. You can buy Knowledge Ranks as Cross Class Skill, if neccessary.

Mustrum Ridcully

 

[Kae'Yoss]

The "untrained" descriptor simply states wether you can use the skill without any ranks in it. For example, you can attempt to move silently without having a single rank in it. It has nothing to do with cross class skills.

A cross class skill is simply a skill that you must buy at double price and can only be half as good at as at a class skill. A wizard 7 can have 10 ranks in spellcraft, a fighter 7 only 5. The wizard pays 1 skill point per rank, the fighter 2.

If a skill cannot be used when it's not on your class list, it's called exclusive. That includes use magic device. A rogue 7 can have 10 ranks in UMD, but a fighter cannot have a single rank.
If the exclusive skill could be used untrained, you still would be able to use the skill (it would effectively be an ability check). That's how Scry works afaik: a rogue could use a scroll with a divination spell on it (with UMD), and could make that scry check mentioned in the spell description, even if he hadn't ranks in it.

 

[Umbran]

If a skill cannot be used when it's not on your class list, it's called exclusive.

Not quite.

A skill is exclusive if you must have a specific class to purchase ranks. While in most cases exclusive skills cannot be used untrained, it isn't always so. In the core rules there is one exception, and the DM may have others.

Scry, for example, is exclusive to Bards, Clerics, Druids, Sorcerers, and Wizards. A fighter or rogue cannot purchase ranks in the skill. However, Scry can be used untrained. The fighter can try to make a scry check without any ranks in the skill, basing off his raw Intelligence.