Subjective modal verbs (speaker's stance)

What it is: Subjective modal verbs mark the speaker's stance rather than objective ability or obligation: either a degree of certainty (epistemic) or the attribution of a claim (reportative).

The two functions:

• Epistemic (probability): muss/müsste (near certain) > dürfte (probable) > könnte/kann (possible) > mag (concessive). Example: Sie müsste längst angekommen sein. (She must have arrived long ago.)
• Reportative (source of a claim): sollen = a third party claims it (often a rumour): Das Medikament soll helfen. (The medicine is said to help.) wollen = the subject claims it of itself (often doubted): Er will nichts gewusst haben. (He claims to have known nothing.)

Examples:

• Der lange verschollene Forscher soll in einem Dorf gesehen worden sein. - The long-missing researcher is said to have been seen in a village.
• Das dürfte stimmen. - That is probably correct.
• Der Zeuge will alles gesehen haben. - The witness claims to have seen everything.

Common mistakes: Keep sollen (others claim) distinct from wollen (the subject's own, doubted claim). Do not confuse subjective muss (a logical conclusion: "must be the case") with objective muss (obligation: "has to do it"). The past uses haben/sein + Partizip II + Modal-Infinitiv.

Modal verbs used not for objective ability/obligation but to mark the speaker's stance: degree of certainty, or attribution of a claim.

Epistemic scale: muss/müsste (near certain) > dürfte (probable) > könnte/kann (possible) > mag (concessive). Reportative: sollen = a third-party claim („Das Medikament soll helfen“); wollen = the subject's own (doubted) claim („Er will nichts gewusst haben“).

Modalverben drücken nicht objektive Fähigkeit/Pflicht aus, sondern die Haltung des Sprechers: Grad der Sicherheit oder Quelle einer Behauptung.