Do Cittamatra / Yogacara explicitly refute the existence of an external world? Tibetan texts that belong to the genre of tenets (doctrinal classification) usually claim that the Cittamatra school refutes external existence. These texts further claim that Cittamatrin posit that 'the apprehended object and the apprehending consciousness are empty of being different substances'. They say that, according to Cittamatrin, the apprehending consciousness and the object it apprehends both arise simultaneously from a seed that was left in the mind-basis-of-all (alaya-vijñana), and that, given so, the object is not a cause of the consciousness apprehending it (as opposed to what Vaïbashikas and Sautrantika posit). Jetsün Chökyi Gyaltsen writes:


  An illustration of the selflessness of phenomena is, for example, the
  emptiness that is a form and the valid cognizer apprehending that form
  being empty of being different substances.



It is difficult for me to conceive, and to admit, that Cittamatrin refute external existence altogether. It would mean they refute that one is born from a mother and a father, and so forth. Moreover, I doubt Tibetan scholars who claim that 'Cittamatrin refute external existence' because they have an agenda. Tibetan scholars often simplify (if not even caricature) their opponent's positions (in this case, Cittamatrin). So, not sticking to Tibetan literature only, my idea was to seek whether Cittamatrin actually refute external existence by reading works written by proponents of the Cittamatra school. Let us consider Suzuki, in Studies in the Lankavatara (p. 114). He writes:


  As indeed the idealistic Mahayana does not admit the
  existence of an external world, whatever qualities we ordinarily think
  as belonging to the latter are creations or constructions of our own
  mind.


Suzuki seems to say "Cittamatra refute external existence", but he does not do so explicitly. He says "they do not admit the existence of an external world" but this does not necessarily amount to "refuting the existence of external world". As far as I know, he could be saying "We can not know anything but the aspects our consciousness takes. We can not see beyond our perceptions. We can not know for sure whether our perceptions are perceptions of something external. So, let us not bother with thinking of an external world - be it to refute its existence or claim its existence - and let us stick with what we know: that the eye-consciousness seeing blue takes the aspect of blue, and that we know nothing else."



Thus, the question is: Do Cittamatra / Yogacara explicitly refute the existence of an external world? Or do they simply "not admit, not take into acount" the existence of an external world?

References are welcome.
According to Kagyu understanding, Yogacara's position isn't metaphysical, it is methodological. It's not that the external world does not exist, it is that our experience of the world is 100% always represented by organs and/or mind, there is no experience outside of that, so practically speaking mind-made experience is "all we have"*

Which is why trying to figure out how exactly the experience is generated and mastering the practical skills for working with mind and experience is of key importance in Yogacara (comparing to the earlier Buddhism's focus on discipline/ethics and the Madhyamika's focus on philosophy).


  Yogacarins put so much emphasis on the mind because they are concerned with
  practice. Some people have thought they were saying that everything is in your
  mind. Some of these people were influenced by certain Western philosophies.   -- Traleg Kyabgon Rinpoche 


Generally speaking Kaguypas seem to prefer to stay away from philosophical discussions and focus on practice, which makes sense given their self-identification as "the practice lineage":


  We are not concerned about whether or not a chair exists. That's
  secondary. Why spend so much time arguing about whether or not a chair exists,
  instead of learning how we experience and relate to the chair, and what sort of
  experience we've got? -- Traleg Kyabgon Rinpoche




*Using the modern language we could say, reality is an interpretation we make, there is no reality to be experienced outside of an interpretation. In other words, there is no absolute truth separate from the conventional truth.