Having a claim to a title means you've got a justification for it being yours. Claims come in two varieties, weak and strong. Claims are used as Casus Belli for war. The difference between a strong and a weak claim can be determined by the graphics, and mousing over a claim will indicate whether it will currently be inherited.
Strong claims are, as the name implies, the most useful type of claim. A strong claim can be pushed against anyone by almost anyone. The exception is that you cannot push a vassal or courtier woman's claim upon a title if the title uses Agnatic succession law (If you are female, you may however press your personal claims no matter what the succession law is). Only the second and third in line to a title will get strong claims upon the titleholder's death. (There is one exception: under gavelkind succession, the primary heir does not get claims on titles that are passed to his siblings if they become his vassals, although he does if they become independent.)
Strong claims can also be gained via the Fabricate Claim councillor mission as well as the Forge Claim plots. A character who loses a title (through war or intrigue) will also get a strong claim on their former territory. The Pope can also grant Catholic rulers claims on counties or duchies if he dislikes the current holder.
Children of strong claim holders inherit weak claims. The one exception are claims granted by the councillor mission, which are not inherited unless pressed in war.
A weak claim can only be pushed if:
- title is held by a woman and the claimant is not
- realm is in a regency due to prison, incapability, or youth
- a succession crisis is ongoing
- or claimant is 2nd or 3rd in line to the title.
Like with strong claims, you cannot put a woman on a throne if the succession is Agnatic. All children (unless 2nd or 3rd in line) of a titleholder get weak claims upon the titleholder's death, and their children can inherit the claim, and they can be inherited from holders of strong claims. The claim has to be pushed if the children's children are to inherit the claim.
- 2nd or 3rd in line to a titleholder: strong, inheritable claim
- Other child of a titleholder: weak, inheritable claim
- Children of holder of inheritable claim: weak, uninheritable claim
- Fabricate Claim mission: strong, unheritable claim
- Forge Claim plot: strong, inheritable claim
Pressing a claim
A claim is "pressed" when war is declared using that claim as a casus belli. Pressing a claim "renews" it, ensuring that it will be inherited by the claim holder's children. Even if the war ends in white peace or inconclusively, the claim remains pressed. It is sometimes useful to press a claim of a courtier and then get white peace, so that that courtier's children - belonging to your dynasty, perhaps - will inherit the claim.
Multiple claims against a single opponent may be pressed in a single war, but only if they're all held by the attacker; you can only push a single claim by someone else at a time.
When viewing a title, clicking the "show claimants" button will display a list of all claim holders, together with an icon indicating whether they will accept an invitation to your court. Note that this display does not distinguish between strong and weak claimants, nor does it show characters who will get claims upon the deaths of their parents but do not presently have them. To find potential claimants, try looking at the family tree of the dynasty that holds the title.
Impact of claims on AI
Your AI vassals with claims on one of your titles will have a lower opinion of you. Additionally, the AI is much more reluctant to release a prisoner with a claim on their title.