Here is a small problem with 'credo', there is an example in my dictionary saying that 'crede mihi (dat.)' means 'believe me'.
Gildersleeve & Lodge gives credere under Dative with Intransitive verbs - "The Indirect Object is put in the Dative vith many Intranitive verbs of Advantage or Disadvantage, Yielding and resisting, Pleasure and Displeasure, Bidding and Forbidding."
When I look now this sentence in Spinoza,
Nam quandoquidem ejus essentia omnem imperfectionem secludit absolutamque perfectionem involvit, eo ipso omnem causam dubitandi de ipsius existentia tollit summamque de eadem certitudinem dat, quod mediocriter attendenti perspicuum fore credo.<
..., quod (that) mediocriter (moderately) attendenti (Pr. part. dat.) perspicuum (acc. adj.) fore (Fut. inf.) credo (here as Verba Declarandi, takes inf. and acc.).
'Attendenti' looks to be dative, but could it be here in dative not because of the first, "Dative with intransitive verbs" but because of Dative with Transitive verbs - "The Indirect Object is put in the Dative with Transitive verbs, which already have a Direct object in the Accusative. Translation to, for, from. " (Gildersleeve & Lodge) ? Is it possible that one verb can be intransitive and transitive in the same time, depending of the exact meaning?
When translated "I believe that it would be clear to moderately attentive" - which sounds reasonable in English, but when looking at that first example given, 'crede mihi' then I would think 'quod perspicuum' should be in Dative instead of 'attendenti ' ?