The thing which gets you perplexed is the plot of the movie 'Inception'. The more number of times you watch the movie the lesser sense it makes and you would start finding many Plotholes. Let's do a deep dive into one of the most controversial movie endings.
SPOILER ALERT : Please watch the movie before reading this post since this contains many spoilers.
The Movie doesn't provide a closure for audience as the movie ends before one could know whether Cobb's Totum kept spinning or eventually stops. This boils down to the question : Whether Cobb is still dreaming or is in reality ?
According to me, the climax of the movie depends on the actual definition of “Limbo”.I think the movie provided contradicting definitions of Limbo on multiple occasions :
1) Definition 1 : In Level 1 Dream Conversation when Ariadne asks “How Long could we be stuck there” , Yusuf says “Can’t even think of trying to escape until the sedation is eased”. That means you cannot get out of Limbo even if you kill yourself.
2) Definition 2 : In other conversation Cobb explains that when you die in Limbo then you would wake up straight back in reality ( No Clarity provided on whether it is the case even if you are sedated strongly or not) . If you manually/voluntarily enter Limbo then you could retain the knowledge that you are still dreaming and dare to kill yourself to wake up in reality.
If Definition 1 from Yusuf is correct then many things in the movie makes sense :
1) Cobb and Mal were able to come out of the Limbo not because they killed themselves , it is because the sedation was eased and they had spent good amount of time growing old in Limbo.It might have been just a co-incidence that them killing themselves and sedation easing off happened at the same time.
2) At the end of movie , when Saito and Cobb realize this is a dream and presumably killed themselves , they wouldn’t have woken up in reality because the sedation wouldn’t have yet eased. So Cobb was still dreaming.
If Definition 2 of Limbo is correct, then the climax would end in “reality” and there would be a lot of Plot holes which requires a lot of assumptions and justifications.
Conclusion : So I would just assume that Yusuf’s understanding of Limbo is correct since he is the chemist and knows the facts about the sedative & it’s impact on human brain. Cobb’s understanding of Limbo is wrong and the climax of the movie is that Cobb is still dreaming.
If you are interested in understanding the complete plot of the movie then please read this amazing breakdown and analysis by my friend Sameeran Rao : https://themoviecourt.wordpress.com/2018/12/01/movie-primer-inception/
