Presumed without analysis.
Self-evident, intuitively obvious.
Based on hypothesis and theory rather than experiment or empirical evidence.
Developed entirely from scratch, without deriving it from existing languages.
In a way based on theoretical deduction rather than empirical observation.
Unclear or unreliable.
Experiencing or showing doubt, sceptical.
Subject to, or causing doubt.
Improbable or unlikely.
Suspicious, or of dubious character.
Undecided or of uncertain outcome.
A doubtful person or thing.