Existentialism seems illogical to me. From where does logic receive its terms? Once it has them it can only manipulate them reductively. That is, by dividing what is said in them between 'is' and 'is not' into ever more finely drawn categories. But the rules applied in this have no ultimate truth or "self-evidence" other than our ability to recognize in each other the honesty and discipline of judgement and respect for each other in that judgement. That is, there is no synthetic reason. This opens the way for some to just make stuff up, as logicians do routinely, and call it truth. But they have to rig the conditions in order to get away with this. Existence cannot be rigged. For instance, the law of contradiction is only true a priori under the auspices of pertinent quantifiers. Some are - none are, all are, one is not, and so forth. But this is truth by definition, a circular argument, and the subject and predicate are irrelevant. What "A is B" might really mean, logically, is a complete and total mystery. Unless, that is, the ultimate product of the reductive function logic always is is the complete transformation, even if only in the minutest nuance to our ability to sustain our commitment to it, of all terms. That revision of the terms of reason is a drama subterranean to the conventional laws of reason. But if it comes as product of keeping faith with that law it cannot be untruth. And if it is the only real source of terms, if it is the only valid synthesis, it is hardly illogical to put in the effort to understand it, even though that effort is fraught with error and misdirection. But nothing can be more conducive to error and misdirection than to apply a patently invalid standard as the measure of being reasonable. The fact of the matter is there is no validity in experience and there is no truth in logic. We cannot validly derive anything from experience without appealing to the rational, and logical extensions are only valid or invalid, there is no truth in logic. We need both, and we need each other, to do either. We need existentialism to be logical.