Opposing dogmatism or rigid adherence to established doctrines; characterized by flexibility and openness to new ideas.
From antidogmatic + -al (adjective suffix). This is simply an alternative form of antidogmatic that appeared in 18th-19th century philosophical writing.
The -al ending might seem redundant, but older writers often added it for emphasis or stylistic variation—antidogmatical sounds more formal and philosophical than the simpler antidogmatic!
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