In the scene in Star Wars: The Force Awakens where Kylo Ren is talking to the burned and disfigured mask of Darth Vader, he pleads with this icon to:
Show me again the power of the darkness, and I'll let nothing stand in our way.
While it seems to be a commonly held idea at this point that he's simply talking through his feelings to himself, and there is no evidence in the film that Vader responds to him in any way, the line leads me to wonder if Kylo Ren is actually communicating with the spirit of Vader in some way, or at least has communicated with him in the past.
I realize that Vader's redemption at the end of Return of the Jedi, as well the canon that says that Anakin Skywalker was somehow accepted into the Force and given the ability to return as a Force Ghost would seem to preclude this in many ways. However, I have to wonder if some vestiges of the Sith Lord were left in the currents of the Force, and these remnants are what Kylo Ren is attempting to commune with.
I would prefer current canon answers, but if there is something identified in Legends that explicitly explains this, I'd like to hear about it.
EDIT: While I understand the proposed duplicate, I believe the question to be different as I am asking whether or not Kylo Ren is actually able to communicate with Darth Vader, as it seems to me may be the case.
Based on my reading of the proposed duplicate question (Why hasn't Anakin Skywalker's Force Ghost advised Kylo Ren?), it seems to be asking (and discussing) the reasons why Anakin Skywalker (Light-side) has not attempted to contact Kylo Ren in an effort to dissuade him from his dark path. While there may be some cross-over in some of the answers (such as the link to the article identifying the proposed half-light/half-dark Force Ghost), I still think this is a separate question.
EDIT 2: As further clarification of my perceived difference between this question and the proposed duplicate, that one appears to be more of a question about Anakin contacting Kylo, while this is more about Kylo contacting Vader (or possibly some other Dark Force entity, which brings up some interesting possibilities). Perhaps the question could or should be rephrased, "Is Kylo Ren really talking to himself?"
EDIT 3: One other argument for the possibility that Kylo Ren is doing more than just "talking through his struggle with the Light-side" is that he has shown himself to possess certain Force abilities that have not been seen in other Jedi/Sith in the movies (I don't know if they appeared in EU/Legends works). For example, freezing a blaster bolt in mid-air and hold it there "indefinitely", as well as completely immobilizing his enemies. Vader was able to Force-choke an opponent into submission, but they could still move in reaction (grasping at their throats, etc.). Nearly all Jedi/Sith could deflect blaster bolts with their lightsabers, and Yoda could absorb Force-lightning, but they were all still in motion.
Since Kylo Ren is able to do things that are apparently outside of the normal scope of most Jedi/Sith abilities with the Force, I am left wondering if this scene is something of a souped-up, Force-powered séance or "Ouija board" type experience where he is actually communing with Vader (or, as I stated above, some other entity from the Dark side of the Force), or possibly directly with the Dark side of the Living Force.
EDIT 4: Alright, so after reading the question about Have Kylo Ren's Force abilities been shown before?, it seems that there may be some basis for Kylo Ren's abilities in other works outside of the movies (referenced as Force stasis as seen in the Knights of the Old Republic video games, although I can't find a Wookieepedia reference for this ability). Even so, this does not appear to be a "common" ability used by other Force practitioners, so I would contend that it is still something that is somewhat unique to Kylo Ren and his specific training in the Force.
EDIT 5: Okay, so I'm still searching around, and I found this quote apparently from the Alan Dean Foster novelization posted in another question (What does Kylo say in the English version (and in the other translations) of “Star Wars: The Force Awakens”?) that only fuels my question further:
The alcove where Kylo Ren was kneeling and speaking was darker than the rest of the adjoining chambers. He kept it deliberately so, as seemed appropriate for its function. He spoke now in a tone different from the one he usually employed when conversing with others. There were no orders to be issued here, no pathetic underlings to command. The one with whom he was presently communing would understand everything Ren chose to say, in whatever voice he chose to employ. No need here and now for intimidation, for fear. Kylo Ren spoke, and the object of his words listened in silence.
“Forgive me. I feel it again. The pull to the light. The Supreme Leader senses it. Show me again the power of the darkness, and I will let nothing stand in our way.” Alone in the room, Kylo Ren—saturnine of aspect, lithe of build, tortured of mien, and troubled of eye—gazed at the silent recipient of his confession. [...SPOILER REMOVED...]
Trembling slightly, he rose from where he had been kneeling and strode off to another portion of his private quarters. There was no response from the one to whom he had been talking: neither argument nor agreement. Only silence from the shape that had been the object of Ren’s fervor: a ghostly, deformed mask that had once belonged to another. To a figure of rumor and legend and fear. Misshapen and malformed as it was, no one who had once laid eyes upon the countenance that had belonged to Darth Vader would ever forget it.
While it's explicitly stated that he receives no response, the way that this is worded, IMHO, leaves the possibility open that Kylo Ren is, in fact, making contact with someone or something.