Verbs of Perception and Causation

A small but high-frequency group of German verbs lets you stack one action inside another without any connecting word. Verbs of perception (sehen, hören, fühlen, spüren) and the causative verb lassen take a bare infinitive — an infinitive with no zu in front of it — and the subject of that embedded infinitive lands in the accusative. This page explains the construction, why the accusative appears, and the trap that catches almost every English speaker: in the Perfekt, these verbs do not use their participle but a second infinitive (Ich habe ihn kommen sehen, not gesehen).

Perception verbs + bare infinitive (the AcI)

When you perceive someone doing something, German lets you express both the perception and the action in one clause: the perception verb is finite, and the perceived action sits at the end as a bare infinitive.

The key word here is ihn, not er. The person doing the embedded action is grammatically the object of the perception verb — you see him — so it takes the accusative, even though logically he is the one who is coming. Latin grammarians named this pattern the accusativus cum infinitivo (the AcI, "accusative with infinitive"), and the label is still used for German. The whole stretch ihn kommen is what you see.

English does almost the same thing — and that is precisely why it feels easy until the Perfekt arrives. After see, hear, feel, watch, English also uses a bare infinitive (I saw him leave) or, alternatively, an -ing form (I saw him leaving). German has no progressive participle here, so it always uses the plain infinitive: Ich sah ihn gehen covers both I saw him leave and I saw him leaving.

Causative lassen + bare infinitive

Lassen is the workhorse of German causation. With a bare infinitive it covers a range that English splits across three verbs — have, make, and let — depending on context.

(a) Causative "have / make someone do something." You arrange for an action to happen; someone or something else carries it out.

Notice that Ich lasse mein Auto reparieren leaves the agent (the mechanic) unmentioned — exactly like English I'm having my car repaired. German does not need a passive or an extra clause; lassen + bare infinitive does the whole job. If you want to name the agent, you add it in the accusative or with von: Ich lasse den Mechaniker das Auto reparieren (I have the mechanic repair the car).

(b) Permissive "let someone do something." Here lassen means allowing, not arranging.

sich lassen + infinitive = "can be done"

A reflexive twist on lassen produces a tidy passive-like meaning: sich lassen + infinitive says that something can be done — it is feasible, possible, or open to being acted on.

This construction is a stylish alternative to the werden-passive with können: Das kann gemacht werden and Das lässt sich machen both mean "that can be done," but the sich lassen version is shorter and sounds more idiomatic in speech.

The Perfekt: the double infinitive (Ersatzinfinitiv)

This is the rule competitors gloss over and learners get wrong. Perception verbs and lassen normally form their Perfekt with a Partizip II (gesehen, gehört, gelassen). But when they govern a bare infinitive, the participle is replaced by a second infinitive — the Ersatzinfinitiv ("substitute infinitive"). The two infinitives pile up at the end of the clause, and the order is fixed: the main verb's bare infinitive first, the perception/causative infinitive last.

Why does German do this? The participle marks an action as completed and bounded, but here the perception verb is not the focus of completion — it is just framing another action. German resolves the awkward clustering of two non-finite forms by levelling both to infinitives, the most neutral verb shape. The same mechanism powers the Perfekt of modal verbs (Ich habe arbeiten müssen, not gemusst), which is why the two topics are taught together.

A caution on fühlen and spüren: although fühlen technically allows fühlen as the Ersatzinfinitiv, in practice German speakers strongly prefer the regular participle gespürt / gefühlt with a wie-clause in the past: Ich habe gespürt, wie mein Herz schneller schlug sounds far more natural than Ich habe mein Herz schneller schlagen fühlen. Sehen, hören and lassen are the verbs where the double infinitive is genuinely standard.

A note on machen

English speakers reach for "make someone do something" and try to translate it with machen — but causative machen + bare infinitive is not standard German. To say "make someone do something" you use lassen, bringen ... dazu, or veranlassen.

Note that bringen ... dazu and veranlassen switch to a zu-infinitive — they are ordinary verbs, not bare-infinitive verbs. Only lassen and the perception verbs take the bare infinitive.

Common Mistakes

Key Takeaways

• Perception verbs (sehen, hören, fühlen, spüren) and causative lassen take a bare infinitive — never zu.
• The subject of that embedded infinitive is the accusative object of the main verb: Ich höre *ihn singen*.
• In the Perfekt, the participle is replaced by a substitute infinitive (Ersatzinfinitiv): habe ... kommen sehen, habe ... spielen hören, habe ... reparieren lassen.
• The two infinitives cluster at the clause end in the order [embedded action] + [perception/causative verb].
• For "make someone do something," use lassen — not machen. Bringen ... dazu and veranlassen switch to a zu-infinitive.