The Rishonim are bothered with the halacha of not being allowed to say psukim by heart, since we find many people saying pesukei d’zimra and kriyas shema by heart. There are many answers found in the Rishonim, and all are brought in the Poskim. 1. If it is fluent by people it is permissible, (therefore pesukei d’zimra, krias shema and bircas kohanim are permitted). 2. ‘עת לעשות לה since it is difficult for everyone to have a sefer or siddur it is permitted. 3. Tefillah is permissible. 4. Only when being motzi others is it prohibited. 5. If it is part of the סדר היום it is permitted. 6. The entire Halacha is only a מצוה מן המובחר and therefore permitted for the honor of the ציבור (for example speaking to the public and difficult to read from inside a sefer). 7. The prohibition is only on psukim in the chumash. 8. Something that is said as a chovah is permitted even when not said for a chovah. 9.Only things said as a חובה are prohibited. 10. Only with the טעמים is it prohibited. 11. For the ציבור it is permitted, and these things are permitted even with the yachid. 12. What is for praise and thanks for Hashem is permitted.