Breaking line of effect

[Berengar]

@"ArM5 p.80 [i

The Limit of Arcane Connection[/i]"]Hermetic magic cannot affect an unsensed target without an Arcane Connection. This is widely believed to be a flaw in Hermetic theory, as Intellego magic is much less tightly bound by this limit than other kinds. Intellego can determine whether, for example, there are any people behind a wall the magus can see, but Perdo Corpus magic cannot affect those people until the magus is aware of them.

So it is a magus' awareness of something, which allows him to target it without an AC.

While a spell with R: Sight requires seeing the target, sensing the target of a magic spell or effect does not.

See for example

@"TMRE p.94f [i

New Range: Line[/i]"]The advantage of Line Range is that it extends as far as Sight but does not require that the magus can see the target. However, he must be able to sense it in some other fashion: Hermetic magic cannot in general affect an unsensed target. For instance, the magus may hear someone talking on the other side of a wall.

You can instead see the plants move while the target animal pushes through shrubbery, or the tracks it leaves in the snow on the ground. And you can also target an animal which you just locate from the noises it makes - like winnowing or beating the ground with its hooves. All that is sensing it.

Note, that MoH p.101 To See as Through a Plethron Distant, which magically recreates species, does not extend the targets for spells. Hence ArM5 p.127 Eyes of the Bat, which also magically creates species, should neither.

Cheers