The paper by Steven Weinberg applies effective field theory methods to study generic theories of inflation with a single inflaton field. For scalar modes, the leading corrections to the $\mathcal{R}$ correlation function are found to be of the $k$-inflation type, while for tensor modes, the corrections arise from terms in the action that are quadratic in the curvature, including a parity-violating term affecting the propagation of these modes. The methods are also briefly applied to non-generic theories with an extra shift symmetry, such as ghost inflation. In the generic theories of inflation, the Lagrangian is described by a scalar field $\varphi_c(x)$ with a potential $V(\varphi_c)$, and the cosmic expansion rate $H$ and the physical wave number $k/a$ at horizon exit are determined by the slow-roll parameters. Weinberg assumes that the Lagrangian is the first term in a generic effective field theory, where higher derivative terms are suppressed by a large mass $M$. The leading correction term involves generally covariant terms with four spacetime derivatives and coefficients of order unity. For scalar fluctuations, the leading corrections to the Gaussian correlations of $\mathcal{R}$ are solely of the $k$-inflation type. For tensor fluctuations, the corrections depend on the helicity of the modes due to parity violation. The paper also discusses a non-generic example of ghost inflation, where the Lagrangian density involves only spacetime derivatives of the inflaton field, and the characteristic mass $M$ can be much smaller than in generic theories.The paper by Steven Weinberg applies effective field theory methods to study generic theories of inflation with a single inflaton field. For scalar modes, the leading corrections to the $\mathcal{R}$ correlation function are found to be of the $k$-inflation type, while for tensor modes, the corrections arise from terms in the action that are quadratic in the curvature, including a parity-violating term affecting the propagation of these modes. The methods are also briefly applied to non-generic theories with an extra shift symmetry, such as ghost inflation. In the generic theories of inflation, the Lagrangian is described by a scalar field $\varphi_c(x)$ with a potential $V(\varphi_c)$, and the cosmic expansion rate $H$ and the physical wave number $k/a$ at horizon exit are determined by the slow-roll parameters. Weinberg assumes that the Lagrangian is the first term in a generic effective field theory, where higher derivative terms are suppressed by a large mass $M$. The leading correction term involves generally covariant terms with four spacetime derivatives and coefficients of order unity. For scalar fluctuations, the leading corrections to the Gaussian correlations of $\mathcal{R}$ are solely of the $k$-inflation type. For tensor fluctuations, the corrections depend on the helicity of the modes due to parity violation. The paper also discusses a non-generic example of ghost inflation, where the Lagrangian density involves only spacetime derivatives of the inflaton field, and the characteristic mass $M$ can be much smaller than in generic theories.