Nope. They actually fit together surprisingly well. Yes, the Idea of Ideas does speak about truth, and Agrippa’s Trilemma reminds us that truth cannot be fully and finally justified from within human thought alone. But that does not hurt the framework. It helps define its limits.
Agrippa’s challenge is fascinating, but it also blurs important categories. It treats justification too generally, as if all truths must be grounded the same way. That is not the case. Empirical ideas are grounded in observation and measurement. Rational ideas are grounded in logic and internal consistency. Irrational ideas are speculative or disproven. Some are untested, untestable, some are inconsistent, and some are empirically disproven. Mixing these categories together creates the very confusion Agrippa exposes.
Agrippa is mainly talking about ultimate justification, not truth itself, and not certainty. That matters. The Idea of Ideas is doing something different. It sorts ideas by how they relate to reality, how they are formed, and how far they can be trusted.
So where do the two meet?
Agrippa tells us that final philosophical justification runs into a wall. The Idea of Ideas says, of course it does. That is why we must keep a clear split between reality itself and our ideas about it. Absolute truth belongs to reality. Human truth belongs to our descriptions, measurements, and rational models of it.
Empirical ideas do not defeat the trilemma so much as they are anchored by the world. Rational ideas do not defeat it either; they hold by internal coherence within a system. Irrational ideas fail on both fronts. So Agrippa does not disprove the Idea of Ideas. He highlights why such a framework is needed in the first place.
