Let's begin by defining our terms. A soliloquy is a relatively long speech given by a character who stands alone on the stage talking to themselves or the audience. A monologue, on the other hand, is a relatively long speech delivered by one character to other characters. In an aside, a character speaks to themselves and/or the audience while other characters are on stage; the other characters do not hear the words of the aside. With those definitions in mind, let's pick out the soliloquies, monologues, and asides in Act 3 of Romeo and Juliet.

In the first scene, Mercutio and Benvolio enter, and Mercutio delivers a monologue about Benvolio's hot temper. Later in the scene, after Tybalt kills Mercutio and Romeo kills Tybalt, Benvolio delivers a monologue explaining what has happened and why. At the end of the scene, the Prince speaks a monologue of his own, exiling Romeo from Verona.

Scene 2 begins with a soliloquy from Juliet, who is anxious for night to fall so that she can consummate her marriage to Romeo. Later in the scene, after Juliet finds out what happened between Romeo and Tybalt, she delivers a monologue as she tries to process the fact that Romeo has been banished from Verona.

In Scene 3, Romeo speaks a monologue to Friar Laurence, lamenting his separation from Juliet due to the banishment. Friar Laurence also delivers a monologue as he prevents Romeo from committing suicide and gives him advice about what to do next; namely, go to Juliet as planned and then beg the pardon of the prince.

In Scene 5, Juliet speaks an aside as she talks with her mother. Lady Capulet calls Romeo a villain, and Juliet turns away, asks for God's pardon on Romeo, declares that she has forgiven him, and remarks that he still grieves her heart. Capulet presents a short monologue at the end of the scene in which he decrees that Juliet will marry Paris on Thursday, and that is the end of the matter.

A monologue is a speech that one character gives in the presence of other people. It usually presents their own thoughts or offers a sustained narrative. A soliloquy is also a speech by one character, but they typically deliver it alone onstage. An aside is a piece of dialogue, usually quite short, that a character speaks as if the others could not hear it. Act 3 includes examples of all these dramatic devices.

Scene 1 includes monologues by Mercutio in lines 16–30, Benvolio in lines 156–180, and the prince in lines 192–202. Romeo delivers a short soliloquy in lines 109–115.

Scene 2 opens with Juliet’s soliloquy, lines 1–34, and she also delivers two substantial monologues in lines 76–88 and 102–132.

In scene 3, Romeo speaks a monologue in lines 30–52, and Friar Laurence delivers a long monologue in lines 114–164.

In scene 4, although Lord Capulet speaks at length, he is conversing with his wife and Paris. His lines would not be considered monologues, because he engages the others rather than offering only his own thoughts or ideas.

In scene 5, Juliet’s aside in lines 84–85 is marked by the stage directions. Here Lord Capulet does deliver a monologue; in his speech in lines 184–204, the first half presents his reflections, before he returns to addressing his daughter directly.

The difference between a monologue and a soliloquy is that a monologue is a long speech delivered by one character "who forgets or neglects" that other characters are still present while a soliloquy is delivered when the character is completely alone or at least believes himself/herself to be alone (Dictionary.com). Both monologues and soliloquies express the inner-most thoughts and feelings of the character. Soliloquies can also give the audience vital information (Dr. Wheeler, "Literary Terms").

One excellent example of a soliloquy is Juliet's opening speech in Act 3, Scene 2 in which she pours out her heart about waiting for Romeo and her feelings of anticipation for her wedding night. When Juliet says this long speech, she is alone in her room. Also, the speech shows us all her inner-most thoughts and feelings and characterizes her as growing into a woman; therefore, it is an excellent example of a soliloquy.

An excellent example of a monologue can also be found in Act 3, Scene 2. In lines 102-132, Juliet speaks to try and console herself about Romeo having just killed Tybalt. Even though she addresses Nurse in the first lines, reprimanding Nurse for thinking poorly of Romeo, she says to herself, "Shall I speak ill of him that is my husband?" Also, Juliet loses herself in this speech and talks as if she has forgotten that Nurse is still in the room. The speech becomes a means for her to grapple with her own feelings in order to help her realize that Romeo killed Tybalt because Tybalt was about to kill Romeo. The speech also serves to help her mourn the news that Romeo has been banished, which feels as bad as if all of her family has been slain, as we see in her lines:

'Romeo is banished'--to speak that word
Is father, mother, Tybalt, Romeo, Juliet,
All slain, all dead. (I.ii.127-129)

Hence, even though Juliet addresses Nurse at the beginning of the speech and again at the end, because this speech mostly addresses herself as a means of pouring out her feelings, Juliet speaks as though she has forgotten that Nurse is still present in the room. Therefore, this speech is an excellent example of a monologue.

Similar to a soliloquy, an aside is spoken by one character and it is believed that the other characters do not hear him/her. The differences are that an aside is very short, usually only consisting of a few lines, and also that an aside is directed straight to the audience. In addition, asides are always marked by stage directions while soliloquies are not (Dr. Wheeler, "Literary Terms"). One excellent example of an aside in the third act is spoken by Juliet. When Juliet's mother tells Juliet that she is weeping not so much over Tybalt's death but because Romeo, the "villain," is still alive and has been granted such a soft sentence by the Prince, Juliet addresses the audience with an aside to declare that Romeo is not a villain and that she has forgiven him, as we see in her lines:

Villain and he be many miles asunder.
God pardon him! I do, with all my heart;
And yet no man like he doth grieve my heart. (III.v.84-86)

Hence, we see the differences between monologues, soliloquies, and asides and have identified one of each in Act 3.