The Place of Espionage in International Law

Espionage is often characterised as being both lawful and unlawful under international
law. The present contribution seeks to shed light on such enigmatic references by drawing
on the distinction between strong and permissive rules. If one leaves behind the binary
perspective of the Lotus world which only knows prohibited and non-prohibited (i.e. permissive)
conduct, a more sophisticated vision of the contemporary international order
emerges. When analysing its architecture, one can usefully rely on Wesley N. Hohfeld's
analysis of jural relations and translate his distinction of rights and privileges into the
differentiation of strong and weak permissive rules. While the former constitute genuine
entitlements which other states must not obstruct, the latter preserve a state's freedom to
act, but without depriving other states of the liberty to interfere with the former state's
conduct. By developing a three-layer approach, the contribution argues that, while certain
spying activities may be contrary to international law (e.g. the principle of non-intervention)
and thus prohibited, and other information-gathering operations may be actively
endorsed by international law (e.g. in the law of diplomatic and consular relations and in
arms control), thus constituting strong permissive rules, the lion's share of »normal« spying
activities can be usefully conceptualised as weak permissive rules. Accordingly, by applying
the analytical prism of strong and weak permissive rules, it becomes possible to transcend
the idea that international law is agnostic on spying and to elucidate the twilight within
which espionage often remains in international law scholarship.