What day is it? And, more importantly, why do we even have to ask? The seven-day cycle we adhere to affects the way we think, according to psychologists from the universities of Lincoln, York, and Hertfordshire. Researchers tested how mental representations of the days of the week are constructed and how that leads to confusion about what day it actually is.

Researchers asked participants to list the words they most strongly associated with days of the week. They found that more words were listed for Mondays and Fridays as opposed to the middle weekdays, giving the beginning and end-of-the-week days a stronger identity. Mondays were labeled with negative words, as one would expect, like boring, hectic, and tired. Conversely, Fridays were labeled with positive words like party, freedom, and release. Tuesdays, Wednesdays, and Thursdays carried less meaning, which allowed them to be more easily confused.

Another reason why we don’t confuse Mondays and Fridays as easily as the middle days of the week is that we don’t talk about those days. We tell our co-workers Mondays stink and we wish the weekend was longer, and when Friday comes, we say, “TGIF!” and go out to happy hour and celebrate. People rarely say, “Hooray, it’s Tuesday!” And since we don’t have natural dialogue with those days, it’s much easier for us to get them mixed up.

Forty percent of the study’s participants were unaware of the current day of the week — some thought it was the day previous, while others thought it was the day after, with most of the mistakes coming in the middle of the week. The number of mistakes increased during a holiday week, with more of the participants feeling as if they were a day behind. Participants were also asked to quickly state the correct day of the week, with Monday and Friday being answered much faster than Wednesday.

"The seven-day weekly cycle is repeated for all of us from birth, and we believe this results in each day of the week acquiring its own character,” said lead researcher Dr. David Ellis, from the University of Lincoln's School of Psychology, in a press release.

According to Ellis, “cycles can shape cognition” even if they’re just social constructs. Having a holiday week, which cuts out days of the week, “implies that apparent weekday is not determined solely by the seven-day period of the weekly cycle: Transitions between the working week and weekend also play a role."

“Indeed, more than a third of participants reported that the current day felt like a different day, and most of those feelings were on Tuesdays, Wednesdays, and Thursdays, reflecting the midweek dip in associations attached to different days,” Ellis said.

Source: Ellis DA, Wiseman R, Jenkins R. Mental Representations of Weekdays. PLOS ONE. 2015.