Sentence:  Doubtless, too, both grammarians and philosophers have been aware that it is by no means easy to distinguish even questions, commands, and so on from statements by means of the few and <WSD>jejune</WSD> grammatical marks available, such as word order, mood, and the like : though perhaps it has not been usual to dwell on the difficulties which this fact obviously raises. 
Meaning of the word marked with <WSD> tags:  Naive; simplistic.