Question: Need help with syntax of dsolve for system of differential equations

I have a set of 3 differential equations called "odesys" that I need to solve. I input this line to solve them and I get the following error. 

sols := dsolve([odesys, ICs], {Theta[1](t), Theta[2](t), Theta[3](t)})
Error, (in dsolve) not a system with respect to the unknowns {Theta[1](t), Theta[2](t), Theta[3](t)}
 

I've also tried it using the exact syntax that the thetas are in the equation and I get this error. 

sols := dsolve([odesys, ICs], {Theta(t)[1], Theta(t)[2], Theta(t)[3]});
Error, (in dsolve) required an indication of the solving variables for the given system
 

I don't know even know which error message is better. The equations are second order and non-linear if that has any bearing on anything.