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Speculative reason, sometimes called theoretical reason or pure reason, is theoretical (or logical, deductive) thought, as opposed to practical (active, willing) thought. The distinction between the two goes at least as far back as the ancient Greek philosophers, such as Plato and Aristotle, who distinguished between theory (theoria, or a wide, bird's eye view of a topic, or clear vision of its structure) and practice (praxis), as well as techne.
Speculative reason is contemplative, detached, and certain, whereas practical reason is engaged, involved, active, and dependent upon the specifics of the situation. Speculative reason provides the universal, necessary principles of logic, such as the principle of non-contradiction, which must apply everywhere, regardless of the specifics of the situation.
On the other hand, practical reason is the use of reason to decide how to act. It contrasts with theoretical reason or speculative reason. Some may try and refer to practical reasoning as moral reason but this kind of reasoning actually falls in line more so with theoretical reasoning as it's a contrast of practical reason. This has little to do with what's practical as practicality involves specific action, decision, and particulars which all have a logical undertone without bias toward an ideology. Moral reason finds itself being more malleable in it's spectrum of reasoning and had the possibility of being skewed by faith and belief. This will lead to discrepancies in practicality given the nature of morals being a culture specific outlook and will reduce the practicality in an outcome as each individual has a separate POV and can change the outcome of moral reasoning. Yet there are philosophers who have erected systems based on this distinction. Two philosophers who have done so are Thomas Aquinas (who follows Aristotle in many respects) and Immanuel Kant.