Knowledge

(Intelligence; Trained Only)

Like the Craft and Profession skills, Knowledge actually encompasses a number of unrelated skills. Knowledge represents a study of some body of lore, possibly an academic or even scientific discipline.
Below are listed typical fields of study.

• Arcana (ancient mysteries, magic traditions, arcane symbols, cryptic phrases, constructs, dragons, magical beasts, Incarnum)
• Architecture and engineering (buildings, aqueducts, bridges, fortifications)
• Dungeoneering (aberrations, caverns, oozes, spelunking)
• Geography (lands, terrain, climate, people)
• History (royalty, wars, colonies, migrations, founding of cities)
• Local (legends, personalities, inhabitants, laws, customs, traditions, humanoids)
• Nature (animals, fey, giants, monstrous humanoids, plants, seasons and cycles, Weather, vermin)
• Nobility and royalty (lineages, heraldry, family trees, mottoes, personalities)
• Psionics (ancient mysteries, psionic traditions, psionic monsters, psychic symbols, cryptic phrases, astral constructs, psionic races)
• Religion (gods and goddesses, mythic history, ecclesiastic tradition, holy symbols, undead)
• The planes (the Inner Planes, the Outer Planes, the Astral Plane, the Ethereal Plane, outsiders, elementals, magic related to the planes, Incarnum)

Check

Answering a question within your field of study has a DC of 10 (for really easy questions), 15 (for basic questions), or 20 to 30 (for really tough questions).
Identify Monsters: In many cases, you can use this skill to identify monsters and their special powers or vulnerabilities. In general, the DC of such a check equals 10 + the monster's CR. For common monsters, such as goblins and orcs, the DC equals 5 + the monster's CR. Particularly rare monsters will have a DC of 15 + the monster's CR. A successful check allows you to remember a bit of useful information about that monster. For every 5 points by which your check result exceeds the DC, you recall another piece of useful information.
Identify Monster Components: You can identify the useful and harvestable components of a slain monster with a successful knowledge check (typically 11 + the monster's CR) appropriate to the monster's type. A successful check identifies the presence of and means of removal for all havestable components. A failed check omits one component, plus an additional component for every 2 points by which the check fails. Omitted components aren't necesarrily unknown to you, but the means of removing them without ruining their usefulness are. If you succeed on this check by 5 or more, any Survival checks to remove those components gain a +1 Competence Bonus for every 5 points you succeed by. If another character makes a Survival check to remove a component you identified, they take a -2 penalty to the check as you must relay information to them.

The following aspects of the Knowledge skill may also prove useful.

Arcana: The Knowledge (arcana) and Knowledge (history) skills might be useful in helping to identify command words or deciphering clues regarding magic items. A successful check against DC 30 is needed to come up with the word itself. If that check is failed, succeeding on a second check (DC 25) might provide some insight into a clue.

Architecture and Engineering: If you have a good vantage point to view an enemy stronghold, a DC 20 Knowledge (architecture and engineering) check reveals a weak aspect of the defense. For every 5 points by which your check results exceeds the DC, the DM can give you another strategy tip for assaulting the fortress. If you have an accurate map of the stronghold, you gain a +5 Circumstance Bonus on the check.
This skill also encompasses the science of naval architecture, ship design, and construction techniques for large vessels. To some extent it overlaps Craft (boatbuilding), but boatbuilding is the skill used to build small craft - vessels of size Huge or smaller. Building ships of Gargantuan or Colossal size requires a shipwright, not a boatbuilder, and Knowledge (architecture and engineering) is the signature skill of a shipwright.
Large vessels exceed any normal application of the Craft skill, since they represent the collaboration of dozens or even hundreds of specialists, none of whom possess all the skills necessary to build a ship alone (unlike the boatbuilder, who must know at least a little bit about many related skills such as ropemaking, sailmaking, carpentry, and even ironwork). Instead of having each specialist make separate Craft checks to fabricate individual components of a ship, the chief shipwright simply makes Knowledge (architecture and engineering) skill checks to successfully design and oversee the building of a large vessel.
The DC of your shipbuilding check varies with the ship you're trying to build and the craftsmen and materials you have on hand. The materials required to build a ship are equal to half the ship's indicated price; in addition, you must pay the shipyard workers an amount equal to one-quarter of the ship's indicated price.

• DC: The DC of the Knowledge (architecture and engineering) check to oversee the successful construction of the ship in the normal build time. You can take 10 on this check. You need not be present every day, but you must spend at least one full work day out of every four to oversee the shipbuilding process.
  
• Yard Size: The size of the shipyard necessary to build the ship. You are assumed to have a sufficient labor force of skilled craftsmen dedicated to working on the ship. If the workforce is shorthanded or lacking in skill, take a -2 on your check. If the workforce is extremely shorthanded or completely unskilled, take a -5 penalty on your check. If you have to build your ship from substandard materials, take a -5 penalty on your check.
  
• Build Time: The amount of time it takes to complete your ship. If you choose to take 20 with your skill check, double the build time. If you're trying to complete the vessel as a rush job, take a -5 penalty on your shipbuilding check per month you attempt to cut off the normal build time (no vessel can be reduced to less than one-third the normal time).
  
• Magical Assistance: Use of the proper spells or monsters with especially useful characteristics (for example, a giant) adds a significant bonus on your shipbuilding check. The spellcaster or monster helping you must be on hand at least half the time to give you the bonus. In general, spellcasters must have access to spells of 4th level or better (or a monster must be CR 7 or higher) to count as major magical assistance.

Make a Knowledge (architecture and engineering) check at the end of the specified build time (or sooner, if you're rushing). On a successful check, the ship is ready in the appropriate time. If you miss your check by 5 or less, you fail to complete the vessel on the anticipated schedule. Add one month to the construction time, and check again at the end of the month; if you fail by 5 or less again, you have hit another delay. If you miss your check by 10 or more, the ship is poorly built, and its inherent modifier to Profession (sailor) checks is 5 points worse than the norm for a ship of that type. Fixing a poorly made ship requires rebuilding it, but the build time is reduced by half. If you fail your shipbuilding check to rebuild a poorly made ship, you can't fix it; it will always be poorly made.

Geography: The absolutely crucial tasks of navigation and piloting fall under the description of Knowledge (geography). While Profession (sailor) covers the maneuvering and handling of a ship, the science of navigation requires a distinctly different set of training - mathematics, geometry, optics, and astronomy, among other fields.
Navigation revolves around two basic tasks: course setting and piloting.

• Course Setting: When you set out on a voyage, you need to know how to get where you're going. The difficulty of setting an accurate course depends on the quality of information you have about where you're going. The DM makes this check for you, since you don't know for certain if you have planned an accurate course. You make a course setting check when you begin a voyage, and anytime you realize that you have gotten lost and need to determine a new course to follow to reach your destination.
  If you fail your course setting check by 5 or less, you arrive in the vicinity of your destination; for close voyages, you miss by 5d10 miles; for voyages to distant points, you miss by 5d100 miles. If you fail your course setting check by more than 5, you are wildly off course. On a close voyage, you miss by 10d10 miles; on a long voyage, you miss by 10d100 miles.
  
• Piloting: Piloting is the art of not getting lost and determining where you are in relation to your intended course, so that you can make corrections as necessary. Piloting actually involves a variety of related techniques: celestial navigation, dead reckoning, and true piloting - using landmarks on shore to establish your position. Each day of your voyage, you make a piloting check to establish your position and make the routine corrections necessary to hold to your intended course. The DC of this check depends on the methods available to you; on open ocean with cloudy skies, you have no landmarks and no celestial bodies to observe.
  
  
  Failing your piloting check once is not a problem; you simply failed to establish your location for the day. You can go back to your previous day's established position and estimate your current position given the course and speed you think you've followed since. You do not become lost until you fail your piloting check on three consecutive days. Being lost at sea is much like being lost on land; see the effects of being lost.

History: With a successful DC 15 Knowledge (history) check, you know the basics of how a particular army organizes itself. For example, a successful check reveals that bugbears include a shaman in every 20-soldier platoon, or that elf generals often ride with the cavalry.
If you're standing on or near a historic battlefield, you can recall the details of the battle fought there with a DC 20 Knowledge (history) check. You know, for example, that the dwarves of the Brass Hills defeated the orc hordes by starting an avalanche on the hills to your left, and that most of the surviving orcs retreated into the lava tubes somewhere ahead.
In a military campaign, a character with Knowledge (history) will be well versed in military history and know something of military tactics used in past wars. A DC 20 Knowledge check enables you to provide a strategic advantage to your side in a battle (see Strategic Advantages). Use the guidelines in that section to determine which situations are appropriate for each area of knowledge. As always, the DM is the final arbiter of this issue.
Local: A DC 10 Knowledge (local) check is sufficient to identify a military unit or noble's family by its heraldry, if the unit or the family hails from the local area. A Knowledge (nobility and royalty) check is required to identify the heraldry from far-off lands.
You can use the Knowledge (local) skill to answer questions about various martial practitioners and traditions. For example, you can attempt a Knowledge (local) check to identify a monastic order or swordsage school known to practice a particular martial discipline, to recall basic facts about the philosophy or teaching practices of a particular discipline, or to recall the adventures or exploits of famous martial artists.
Nobility and Royalty: A Knowledge (nobility and royalty) check tells you something about the heraldry of far-off lands. A DC 25 check tells you what part of the world (down to the province or city) a heraldic design comes from. A DC 30 check tells you the name of the military unit or the noble family.
You can use this skill to discover the levels of bureaucracy within a royal household, government, or other large body of authority. If you make a check (DC 15 + organization size modifier), you gain a +2 Circumstance Bonus on Bluff and Diplomacy checks pertaining to that particular organization for one week. However, failure by 5 or more means you make a false assessment of the situation, imposing a -2 penalty on the use of those skills for one week instead. (The DM should make this check in secret, and apply the appropriate modifier when required.) The size and complexity of the organization may provide a bonus or a penalty on this check.
Religion: You can use this skill to understand the structure of authority within a church, cult, or other religious organization. If you make a check (DC 15 + organization size modifier), you gain a +2 bonus on Bluff and Diplomacy checks made during the next week that pertain to that particular organization. However, failure by 5 or more means you make a false assessment of the situation, imposing a -2 penalty on the use of those skills for one week instead. The size and complexity of the organization may provide a bonus or a penalty on this check.

Action

Usually none. In most cases, making a Knowledge check doesn't take an action - you simply know the answer or you don't. Using Knowledge to gain a strategic advantage for a battle requires 1 hour of planning during the planning stage.

Try Again

No. The check represents what you know, and thinking about a topic a second time doesn't let you know something that you never learned in the first place.

Untrained

An untrained Knowledge check is simply an Intelligence check. Without actual training, you know only common knowledge (DC 10 or lower).

Special

Studying tomes, books, scrolls, or other works containing information about the subject of a knowledge check may provide a bonus to said check. Such an action takes time (minimum 1 hour, up to several weeks) depending on the circumstances, and typically provides a Circumstance Bonus to the roll. Doing so may also allow you to reroll a previously failed Knowledge check.

Skill Unlock

A character who selects this skill for the Signature Skill feat or a Rogue who selects it for their Rogue's Edge class ability gains the following abilities when they reach the designated number of ranks in this skill:

• 5 Ranks: When you successfully identify a creature, you gain one additional piece of information for every 5 ranks you possess in that Knowledge skill.
• 10 Ranks: When you successfully identify a creature, you gain a +1 Competence Bonus on attack rolls, opposed ability checks, skill checks, and Caster Level checks against creatures of that kind (e.g., glabrezu demons, but not other demons or evil outsiders) for 1 minute. This bonus increases by 1 for every 5 ranks beyond 10 you possess in that Knowledge skill.
• 15 Ranks: When you fail a Knowledge check, you can reroll the check at a –10 penalty. The Competence Bonus above also applies to Saving Throws against exceptional, spell-like, or supernatural abilities used by creatures you identify.
• 20 Ranks: Whenever you attempt a Knowledge check, you can roll twice and take the better result.

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