He speaks as if he ______ the theory himself, though he barely understands it.

Option 1: had devised ✅

When we use "as if" to describe something not true, referring to a time before the present moment, we use the past perfect tense (had + past participle). He didn't actually devise (create/invent) the theory, but he talks like he did.

Pattern: "as if" + past perfect → for unreal past situations.

Example: "She talks as if she had visited Paris" (but she never went there).

Why not the others?

Option 2: would devise → This suggests something that might happen in the future or a willingness to do something. But the sentence is about him pretending he already came up with the theory, not about something he'd do later.

Option 3: will have devised → This is future perfect tense, talking about something completed at a future point. The sentence isn't about the future — it's about how he speaks now as if something happened in the past.

Option 4: devised → Simple past might sound okay, but after "as if," when describing an unreal situation connected to a time before the main verb ("speaks"), we go one step further back in time using the past perfect ("had devised"), not just simple past.

Hence, Option 1: had devised is the correct answer.