If it’s about what your partner says, thinks, feels, or intends, you can’t unless you ask and your partner is honest.
The following link contains four videos made by actors who were
asked to convey one specific intention through their speech and actions: to be sincere, or to tell ‘white lies’, or to be teasing, or to be sarcastic. (How can I tell if she’s lying?) (emphasis added)
Well-worth viewing, the videos are instructive because they show how difficult it is to grab a single intention from a short segment of speech, or to portray one.
If a single intention is difficult, how can you grab complex intentions from real conversations with real people who are really interacting with you?
You really can’t. Of course, sometimes you will be right, but much of the time you won’t. And if you are wrong just once, your mistake may lead to other mistakes, compounding into something much bigger.
Every day someone is murdered somewhere due to someone else mistaking their intentions. And, I am just as sure, every day many thousands of couples slide toward incompatibility due to accumulating mistakes in their communications.
FIML practice is designed to deal with problems of misspeaking, mishearing, miscogitating, and miscommunicating between consenting partners. FIML practice is based on the recognition that such problems are common, ubiquitous, and inevitable.
A problem with intention—sarcasm, irony, ill-will, etc.—in communication is there is no way to define it or establish any standard for it. With words, we can all agree on rough standards for pronunciation, but when you put a bunch of words together and mix in tone of voice and intention, there arises only an ambiguous standard, at best.
The videos linked above show how difficult it is to isolate even simple intentionality. The communication systems of both listeners and speakers are simply too complex to effectively standardize the majority of normal human communication. If this is understood the value of and reason for doing FIML practice should be clear.