Unobserved

She washed his back and shoulders for him, and whilst she did so, his skin seemed to her to be so fine and soft that more than once, unobserved by him, she touched herself, doubting which of them had the softer and more delicate skin.

Behind the palace, unobserved and free, / there stood a door, a secret thoroughfare / through Priam's halls. Here poor Andromache / while Priam's kingdom flourished and was fair, / to greet her husband's parents would repair / alone, or carrying with tendance fain / to Hector's father Hector's son and heir.

He left the boxes unobserved.

They were counting on sneaking in to the venue unobserved.

Such practices as Theſe, too groſs to lye / Long unobſerv'd by each diſcerning Eye, / The more judicious Iſraelites Unſpell'd, / Though ſtill the Charm the giddy Rabble held, [...]

The relation of the logit formula to the distribution of unobserved utility (as opposed to the characteristics of choice probabilities) was developed by Marley, as cited by Luce and Suppes (1965), who showed that the extreme value distribution leads to the logit formula.